When a person is raised from the dead they lose their original body/race. Instead they are always raised into a new form/race. A DM can take a look at earlier editions of D&D for random reincarnation tables or can look at a 4E reincarnation ritual I did in an earlier article.
Legend: The gods keep the original mortal form as servants while the soul of the character is given a new form.
Almost everyone in the world has a non-combat animal companion. When a person dies his soul goes into his animal companion. From there the person can be raised from the dead as per normal. The only real problem is when a person loses his animal companion; in this case a soul passes on without any chance of future resurrection.
Legend: There have always been mortal ties with the animal/spirit world. This is another way they are bound together.
When any sentient being dies, they rise as an undead. These undead however, are free-willed as they are not created through necromancy. However, they are susceptible to beings that can control undead.
Legend: Long ago a god created the Planar Shield which prevents souls from passing on to the Outer Planes. Thus souls are forced to remain in their bodies as undead.
When a resurrection is cast upon a person’s mortal body, the character must fight a spirit being on the spirit plane. Failure in this fight could mean the resurrection fails or that the character comes back to life with reduced stats.
Legend: The gods do not like the souls in their possession being taken from their realms. This is their attempt to prevent this.
This is not a new idea; it has been mentioned before on the blog-o-sphere. The concept is simply that when a person is resurrected someone else in the world dies. This is a random choice and rarely, if ever, would come into play from a character's viewpoint. However, the concept may cause some moral dilemmas for the characters to work with.
Legend: There are a finite number of souls allowed in the world and a cosmic balance must be maintained.