Afterlife

Bringing Back the Dead

When a creature dies, its Soul departs its body, leaves the Material Plane, travels through the Astral Plane, and goes to abide on the plane where the creature's deity resides. If the creature didn't worship a deity, its Soul departs to the plane corresponding to its alignment. Bringing someone back from the Dead means retrieving the Soul from that plane and returning it to its body.   Enemies can take steps to make it more difficult for a character to be returned from the Dead. Keeping the body prevents others from using Raise Dead or Resurrection to restore the slain character to life.   A Soul can't be returned to life if it doesn't Wish to be. A Soul knows the name, alignment, and patron deity (if any) of the character attempting to revive it and might refuse to return on that basis. For example, if the honorable knight Sturm Brightblade is slain and a high priestess of Takhisis (god of evil dragons) grabs his body, Sturm might not Wish to be raised from the Dead by her. Any attempts she makes to revive him automatically fail. If the evil cleric wants to revive Sturm to interrogate him, she needs to find some way to trick his Soul, such as duping a good cleric into raising him and then capturing him once he is alive again.  
— DM's Guide, p.24
 

THE AFTERLIFE

Most humans believe the souls of the recently deceased are spirited away to the Fugue Plane, where they wander the great City of Judgment, often unaware they are Dead. The servants of the gods come to collect such souls and, if they are worthy, they are taken to their awaited afterlife in the deity's domain. Occasionally, the faithful are sent back to be Reborn into the world to finish Work that was left undone. Souls that are unclaimed by the servants of the gods are judged by Kelemvor, who decides the fate of each one. Some are charged with serving as guides for other lost souls, while others are transformed into squirming larvae and cast into the dust. The truly false and faithless are mortared into the Wall of the Faithless, the great barrier that bounds the City of the Dead, where their souls slowly dissolve and begin to become part of the stuff of the Wall itself.  
— SCAG, p. 20
 

What Is a Soul?

The Soul was the lifeforce of a mortal, the part that gave essence and a separate existence to a creature. In some religions, this lifeforce was variably termed a "spirit", and the two terms were synonymous. In the Mulhorandi faith, this lifeforce was termed two separate spirits, ba and ka. The people of Sokkar referred to this lifeforce as ka. And dragons called their lifeforce an anima.   When a mortal died, its Soul and body were separated, and the Soul automatically began a journey to the afterlife. In the Mulhorandi faith, the ba spirit was said to remain within a mortal's body when they died, while the ka moved on to be judged by Osiris.   In contrast, the case was different for some other kinds of creatures that did not have such a dual nature. For example, some creatures, usually from other Planes of Existence and sometimes referred to as outsiders, did not have a dual nature. An outsider's Soul and body formed a single spiritual existence, tied fundamentally to the essence of its plane. If an outsider died, no Soul left the body. Instead, its essence merged with the plane. Moreover, when such an entity traveled to another plane, it remained anchored to its original plane with a mystical Silver cord. If the visitor to another plane was killed on that other plane, the Silver cord would pull the essence of the creature back, where it would reform into the creature it once was given enough time.   Most Plants, Oozes, and vermin were not sufficiently sentient and thus did not have souls. Undead and Constructs did not usually have souls either, though the creatures from which they were constructed might have.  

The Journey from Life to Death

In Zakhara, a departing Soul was often depicted in the form of a bird, called a hama.   As earlier stated, when en-souled mortals on the Prime Material Plane died under normal circumstances, their souls departed their bodies. They were then pulled to the Fugue Plane. The journey was not instantaneous, although it would seem that way to the Soul itself. Some argued that the journey could take as long as three days to even a month of time on the Prime.   In the land of Zakhara, the departing Soul was called a hama and it often took the spectral form of a bird.   In the teachings of some Draconic religions of Faerûn, the Dragon Soul, the anima did not immediately depart for the afterlife; instead, it was bound to the corpse of the Dragon until the mortal body of that Dragon had completely decayed, freeing the anima for its journey. (In such holy myths, the anima could continue to observe the mortal world but could not interact with it in any other way.)   In some cosmologies, departed souls had to first progress through the Astral Plane. In other cosmologies, the souls were believed to first pass through the Shadowfell on the way to the Fugue.  

Lost Souls

After the Spellplague, souls had to pass through the desolate landscape of the Shadowfell to reach the Fugue Plane. Some souls, for a variety of reasons, never made it to the Fugue Plane. Some became trapped in the Border Ethereal or the Shadowfell as ghosts or other incorporeal undead, visible by other creatures on the Material Plane if the spirit so chose.   A number of other extreme factors could also prevent a Soul from traveling safely to the Fugue Plane, resulting in other forms of undead. For example, a very small percentage of individuals suffering an exceptionally violent murder might result in the Creation of a revenant. A revenant's Soul was unable to reach the Fugue Plane until it had obtained revenge for its death or until a certain time limit had passed. In the lands of Zakhara, it was reported that a Soul, a hama, could be trapped and tethered to the Material in the form of a bird. Such a hama, interestingly enough, somehow remained free of any connection to the Negative Energy Plane and thus was not properly considered a form of undead.   It was also possible to trap a Soul in various magical items. For example, a Ghost lantern utilized an entrapped spirit to generate Light and grant the bearer a limited number of supernatural powers. The greatsword Chalsembyr's Heart entrapped the Soul of its wielder—if the wielder was a noble paladin who died while bearing the weapon—and freed the previous Soul trapped in the blade. The new Soul acted as a guide to the next paladin who bore the weapon in the quest to find the legendary city of Chalsembyr.  

The Fugue Plane

Once arriving on the Fugue Plane, a Soul resided in waiting, wandering about aimlessly, unaware that it had even died, until retrieved by a representative of one of the powers. When—after a time that on Toril would usually correspond to between a day and over a tenday—such a representative arrived, the Soul would always recognize this outsider and would then accompany the being to its final plane of existence to live out the rest of eternity. It was impossible to trick or convince a Soul into following a divine messenger to the wrong god or goddess' realm.   However, sometimes, if a Soul had not been very faithful, it might take centuries for the representative to come. Some souls were said to fade out of existence if a representative never arrived. Others were eventually judged by the lord of the Dead.  

Bargains & Raids

There was one exception to the rule that it was impossible to convince a Soul into following the wrong divine messenger. The baatezu had an agreement that allowed them one final chance to bargain with souls. The baatezu were forbidden to injure or deceive the waiting souls in any way; however, they were permitted to offer them bargains to reject the patron that they worshiped in life in exchange for special benefits in the Nine Hells.   What the baatezu really wanted was more souls with which to create lemures, a form of devil from which more powerful kinds developed, thus building the power of their devilish armies. Most souls would refuse such an offer, of course, but if a Soul had lived an evil life, sometimes the chance to avoid punishment in the afterlife of their deity or to skip a step or two in the hierarchy of the Hells was appealing. Or perhaps the idea of service to the Lords of the Nine seemed better than obeying one's original chosen deity. The most powerful of mortals were sometimes even offered a chance for early promotions to higher forms of baatezu or the promise of some Task or gift to be performed or given on the Material Plane in their behalf—for example, money to surviving relatives or a fiendish act of revenge on enemies.   Souls were a valuable commodity to demons as well, who used them to create the lowest forms of their own kind, the manes. The tanar'ri of the Abyss used a different method to acquire them—they stole them in periodic raids upon the Fugue Plane.  

The Role of the Gods

There had been several gods of the Dead, including Jergal, Myrkul, Cyric, and then Kelemvor, who held sway over this primarily transitory plane.   These gods were those worshiped primarily by Human followers. What of other races? Most races had their own gods or goddesses of the Dead, and each had a special role in guiding the souls of the Dead of that race.   For example, all Dead halflings first had to pass through the realm of Urogalan before reaching their final resting places. The elves of some worlds believed that Naralis Analor, servant of Sehanine Moonbow, was the one who escorted souls from life to death.   Among the Mulan, Osiris was held to be the god of the Dead, the one responsible for dealing out their judgment in the afterlife. How he worked with Kelemvor in this is unclear, but the two were said to be allies.   The Dragon god Null was responsible for shepherding Dragon souls to their final destination. Dragons prayed to Null, asking him to speed the process. Some Draconic myths about the afterlife held that the animae of dragons were not judged by Kelemvor or his predecessors on the Fugue Plane, instead being judged by Bahamut—if good—or Tiamat—if evil—on The Planes of Mount Celestia or Baator, respectively. On occasion, rather than Sending on the anima of an exceptional Dragon to become a petitioner, these rulers of the Draconic pantheon would keep it for their own personal use, to act as a special representative or personal guardian.  

Three Kinds of Mortal Souls

Petitioners
The majority of souls who died from the lands of Faerûn had dedicated their lives to particular power, their patron deity. When these souls were taken by the representative to their deity's divine realm, they were transformed into petitioners.   What happened to a petitioner upon arriving at its final destination varied wildly by which deity that petitioner served. A good number of petitioners appeared much as they did in life, but by no means all. Petitioners of some divine realms took on traits of that realm, such as those of the House of Nature and the Plane of Shadow gaining animalistic or shadowy features, respectively. Petitioners who arrived in the Demonweb Pits lived lives as slaves and appeared similar to Drow. In similar manner, most petitioners of Arvandor, Dwarfhome, The Golden Hills, and Green Fields appeared as elves, dwarves, gnomes, or halflings, respectively, even if they were not those races in mortal life.   Those souls who ended up in the realm of one of the Gods of Fury sometimes took on elemental forms or the forms of wild animals.   Souls arriving in the plane of Limbo were not allowed to manifest in a form but rather were absorbed into the chaos of the plane.   As mentioned earlier, souls stolen by demons became manes and lost all memories of their earlier lives. Manes often did not survive long, but if they managed to persist for many years, they could advance into a more powerful form of demon.   Souls who accepted a bargain with the baatezu most often became mindless lemures in the Nine Hells, but these could be promoted into higher forms of devil. Less sufficiently evil souls were believed to sometimes be made into nupperibos instead.   Most former worshipers of Bane, Beshaba, Hoar, Loviatar, and Talona became Soul larva. Soul larva served as little more than a currency for the Fiendish planes, as they could be transformed into other lower Fiends or simply consumed for power. Petitioners whose journey ended in the Blood Rift had the same fate.   The souls of some noble persons became archons.   Petitioners of Mount Celestia and many within the House of the Triad became lantern archons. Over time, they were promoted into higher forms of archons, namely, hound archons.  
The Faithless
The Faithless were those souls who had never chosen to follow a patron deity or never believed in the gods at all. As such, they would never have a representative sent to retrieve them. Instead, it was mandated that they should enter the City of Judgment to be judged by the god of the Dead. Some believed that the judgment was the same for all Faithless; they became a part of the wall that surrounded the city. Sometimes, the souls were stolen from the wall in tanar'ri raids, but given enough time, a Soul would dissolve into non-existence.  
The False
The False were those who failed to serve their chosen patrons or who had betrayed the commitments to their prior faith. Such souls were also judged by Kelemvor, who assigned them a Task in the City of Judgment for the rest of their existence, such as the guiding of lost souls. The most wicked and unfaithful among the false were actively punished. The majority of the citizens of the City were in fact among the False. The most evil of souls were sometimes transformed into larva and cast out.  

Life After Death

What a Soul did after death also varied based on destination. For example, some souls might live in pure, unadulterated bliss, with all of their needs ever met. Others might suffer in anguish, slaving away in perpetual punishment for the sins of their mortals lives. Still others might engage in epic, never-ending warfare, in a cycle of death in combat followed by rebirth the next morning.   In realms where Corellon and the rest of the Seldarine had sway - such as Toril, elves retained their full individuality, memories, identity and sense of self in afterlife even if their bodies did change.   The animae of Dragon petitioners acted as messengers and servants for the powers that they worshiped.  

Advancement

Petitioners were not static. In some cases, overtime, they changed into new forms. On other planes, they eventually merged with their patron deity or into the essence of the plane itself.   For example, especially good and noble petitioners were sometimes transformed by the will of their Deities into agathinon, the lowest type of angel, forming new bodies for them. Other spiritual entities, such as couatl and ki-rin, where also supposed to have started their existences as mortal souls.  

Reincarnation

Not all souls remained in the afterlife forever. Some elves believed that Sehanine Moonbow worked with Corellon to guide elven souls back to the Material Plane to be reincarnated in a cycle that eventually led to perfection.   All dragons also believed in reincarnation. Their traditions of the afterlife taught that the anima of a Dragon remained on the plane of its deity for a time equal to its mortal life. During that time, its memories and personality slowly faded, one day's worth of memories per day lived in the afterlife, in the opposite order in which the Living Dragon had gained them. When completely stripped bare of the memories of its worldly experiences, the Dragon's anima was reincarnated on the mortal plane as soon as a new mortal body became available. Because the Draconic population in the Realms had decreased over the millennia, however, there was a large "waiting list" of animae ready to be born. These "pure" animae resembled perfectly formed dragons of their species, except that they were trapped in the current moment, unable to form new memories or recall old ones.   Devas were a type of Aasimar whose souls were also perpetually reincarnated on the mortal plane.  

Resurrection

Resurrection was the process of using magic to recall a departed Soul from the afterlife and restore it to its original body. It was easier to raise someone more recently deceased from the Dead than it was to resurrect someone long Dead, because in the former case, the Soul might not have reached its final destination, whereas in the latter case, the Soul would have to be recalled from the realm of a specific deity. For this reason, it was often risky to attempt to resurrect an individual of an opposing alignment; it might anger either the cleric's or the Dead creature's deity!   Once a member of the the Faithless or the False had been judged by Kelemvor, it was impossible for that Soul to be resurrected on the Material Plane by magical spells unless one of the other Deities chose to directly intervene. Such a deity would most likely have to negotiate with the Lord of the Dead.   Not only did the petitioner's god or goddess have to approve of the return to life, so did the Soul itself. A departed Soul always knew the name, moral outlook, and even the chosen deity of the one attempting to call it back to the mortal realm, and the Soul could simply refuse to make the journey back to the Living.   That journey back from the Outer Planes to the Material Plane and the conversion from a petitioner back into a mortal being was a harsh one for a Soul, and most such processes resulted in a lost of memories, skills, and abilities on the part of the one brought back.   The role of memory both before and after death was a tricky one, with conflicting views and opinions among sages. It was said that a Soul that was returned to life after Living part of its existence as a petitioner forgot all memories of that experience in the afterlife. Because the animae of dragons lost memories of their mortal lives in reverse order during their existence as petitioners, a resurrected Dragon would always have amnesia of its mortal life, and the severity of this loss of memory was directly proportional to the time that it had been Dead. In fact, not only was the mind of the Dragon affected but also the physical body. If Dead for long enough, the resurrected Dragon would only have the inherent magical powers of a younger Dragon of its kind!  

Alternate Views of the Afterlife

The illithids did not believe that they would travel to an Outer Plane when they died. Instead, they hoped for their minds to be merged with an elder brain to obtain immortality of thought. It was not clear what happened to the mind flayers' minds or souls if the elder brain were to be slain.   In other Crystal spheres, the rules of death were different. For example, in some cosmologies, the souls of the Dead were said to travel through the divine realm of The Raven Queen in the Shadowfell, before reaching their final destinations.   There are sixteen Outer Planes, all ruled over by Deities and powerful beings. It's common for gods from different campaign settings to share a plane but maintain their own space. Mount Celestia, for example, houses both Heironeous from Greyhawk and Torm from the Forgotten Realms. These planes also contain creatures like angels, demons, and devils, all of which serve the rulers of their respective realms. The sixteen planes (and their corresponding alignments) are:     The true Neutral plane is Outlands which is a separate plane between the 16 other Outer Planes and connects to all of them.         Essentially this is how it works   1) When you die, your Soul goes to the Fugue Plane, a sort of Demiplane where your Soul is taken to the City of the Dead.    
---------------------- 1. The Fugue Plane is only an FR thing, only souls from worshippers of the faerunian pantheon go there   On the Fugue Plane there are three kinds of Soul:   a) Souls who worshiped a deity and lived to the deity's tenets (which are not as tight as some of your examples, I haven't read ever that Tempus for example would refuse a worshiper just because he didn't die in battle, it's just seen as a glorious thing for Tempurians to do): these are called the faithful -> These souls just wait there for a while to be picked up by one of the divine servants sent regular by the respective Deities to collect these souls and bring them to their divine realms   b) Souls who worshiped a deity but did something against the tenets of their deity so that the deity refuses their Soul: these are called the false. -> These people are judged in the City of the Dead and assigned an eternal punishment   c) Souls who didn't worship a deity in live: these are called the faithless -> these are condemned into the wall of the faithless. A otherworldly mortar is holding them in place, while they wither in agony until they are eventually dissolved   Note that if you are a false or faithless you have some last minute opportunity to do a deal with a devil to escape your eternal punishment or the wall, since it takes some time until you are judged (a faithful could also enter such a deal, but most have little reason to do so)   Also demons sometime raid the Fugue Plane and drag souls away (and even break them out of the wall)       For the standard D&D afterlife the Fugue Plane and judgment / wall of faithless part doesn't apply. A Dead Soul is either claimed by a deity it worshiped in live or goes to the plane that most closely matches it's respective shade of alignment   About your points for "why being evil". I think you got all possible reason nice described ---------------------
  2) If your worshiped a God while Living, your Soul is judged according to that God's standards. Every god has a series of requirements, often ritual, that one must fulfill to go to his or her realm. Many of which invoke burial. For example, in my game worshipers of Tempus must die in combat, otherwise they aren't allowed to go to the afterlife, while a worshiper of Mask must have donated a proper sum to his church. Should they fail these requirments, they are condemned to go to their "Rightful" place   3) The Rightful place is one of the alignment planes, either the 9 "Core Planes" or the various mixes of planes, depending on their choices in life. So if I"m a Lawful Good Person, and I either don't worship a god, or I worshiped a non deity faith (like a philosophy or something) or I was heretical in my worship, then I am going to go to one of the Lawful Good Realms (LG, LG/NG/ LG/LN). If I am Chaotic Evil, then I worshiped Bane in the hopes that he would protect me from going to the Abyss, however I failed him (he is a fickle God) and I was rejected from his realm then i'm stuck in the Abyss.   4) Each realm treats your Soul differently. In the Abyss, I am turned into a Soul Larvae, where my Soul struggles to survive and by consuming other Larvae i can eventually become a full Demon and then if i'm lucky rise through the ranks to a Demon Prince (like Orcus). In Hell my memories are wiped and i'm transformed instantly into a Devil, albiet a very weak on on the totem pool . If I go to the Seven Heavens, then I don't have to transform into an Archon, I can stay around in Paradise until I get bored of Paradise and turn myself into an Archon   5) Those who don't worship Gods, and instead follow philosophies, worship native spirits, worship nature itself, or worship a false God go to their AL planes instead.     This helps explain the "Problem of Evil" in D&D, why do Evil people in a world where one KNOWs what the afterlife is like ever be evil?   1) most people don't know how this system works. While people have a general idea of The Planes, the average bandit doesn't know or doesn't care   2) While Absolute Good and Evil are around in D&D, not everybody knows this. Most scholars and clerics are aware of it, but a merchant who cheats people might not be aware that this is how the world works   3) The Vast Majority of Evil People worship Gods, who they believe dictate the "real" absolute morality. So if I worship Hextor, then my world view dictates that I"m not evil, but I am instead a good person protecting the world from disorder   4) Many evil people will go to the afterlives of said Gods rather than going to the Lower PLanes, and thus most mortals don't worry about "not being evil" but instead "trying to be devout".   5) Even those who do know that the Lower Planes exist don't necessarily understand how they function, i'm sure many Lower Plane beings send out massive amounts of propaganda in order to make it seem like a nicer place than it actually is   6) Many evil people believe that if they revere a Demon Lord or Archdevil their master will reward them for their faithful service and will not punish them overmuch going to hell. This is mostly foolish but hey.   7) Finally even those evil people who know full well how the Lower PLanes Work might think that they are so unique that they can overcome it, that because "I" am lord Draken the Lich King, I am inherently powerful enough to rise to the top of the 9 Hells due to my uniquely brilliant mind and abilities.   8) Being Good is really really hard in D&D, and many people just fail to make the cut, Evil is Easier   9) Finally, many evil people might think that they are good. I mean Goblinslayer from the Webcomic "Goblins" clearly though of himself as the Good Guy and didn't realize that torturing Goblins to death counted as an evil action.