Ritual of the Last Flight

If a dragon avoids a violent death, a dragon can theoretically live over 1500 year, but most dragons have their physical strength rapidly deteriorating after roughly 12 centuries.
Most dragons find this intolerable. Besides the fact that for most dragons are not used to physical declines, at this point in their life most dragons have powerful enemies and rivals. They have more treasure than ever before and less might to defend their treasure with.
The Ritual of the Last Flight lets a dragons enter the afterlife on his/her own terms. Dragons are very private creatures in general and they are especially private about their deaths. The details of this rituals are unknown to non-dragons.
It is widely rumored that dragons eat their treasure hoards then ascend to the afterlife directly. Rumor is that the Nine  created a special sub-realm known as the Dragon Graveyard where dragons can go to peacefully end it all and be assured their remains rest in piece.