In the mortal realms, there are many ways that a person can die. Violence, disease, famine and natural causes all contribute to the causes. For mechanics, please see here.
Death's Door (House Rule)Edit
When a character is reduced to zero or fewer hit points (or suffers fatal damage from massive damage), they fall unconscious. They may attempt to stabilize once per round, and lose one hit point if they fail. A character may attempt to stabilize for a number of rounds equal to their Constitution score.
Example: Joe the fighter has a CON score of 17. After falling unconscious at zero hit points, he may attempt to stabilize for 17 rounds. On round 18, he dies.
Once a soul dies, it leaves the body. The varied religions each prescribe an afterlife as a part of their teachings. Worshipers of a faith pass to that afterlife accordingly, so long as proper funerary procedures have been followed.
Agnostic, atheistic, or polytheistic / pantheistic souls pass to a state of limbo. Polytheists and pantheists are claimed by one (or more) of their deities, with multiple claimings resulting in the soul fragmenting (and rendered unable to return to life short of a wish spell) and passing to each afterlife. Unfaithful souls remain in limbo. Those who deny the gods remain awake, but atheists enter a suspended state of slumber in which they are unaware of their surroundings.
Demons, daevas, and deities may claim these souls for their purposes, though the limbo space is under observation by the Progenitors, who ensure that balance remains.