Most faiths address the question of what happens to you when you die, and they come up with a fairly wide variety of answers. Since magic very often involves interactions with the dead it needs to be considered a bit in advance. The GM can select one of them to be true (or make up one of his own), and either insure all the faiths in the campaign believe that or construct some reason why some of them could still be wrong about it in the presence of independent data provided by magic. Or he can assume that all of them are true, and what happens after death is determined by the beliefs of the deceased. In either case the various possible fates do have implications for at least the Path of the Dead. Some of the more common choices are breifly outlined below:
The dead cease to exist. A simple interpretation, but not a particularly popular one historically. In these traditions the Path of the Dead probably does not exist - it is impossible to interact with the nonexistant souls of the dead, and the living probably don't have souls either, though it is not logically impossible. Note if this is true then there is no problem with faiths having widely different versions of what really happens after death, as there will be no contradictory evidence.
The dead remain in the world as spirits - everyone becomes a ghost, and usually continue to live lives more or less like the ones they had before death. This is most often found in cultures with small populations and short historical memories, where nobody would wonder just how crowded the analog of the village in the spirit world is getting. The most common solution to that is to assume it is temporary and assign another fate when nobody alive remembers (or sacrifices to) a particular spirit. In these traditions the dead are easily contacted, at least in their home village, they probably can't be reached in other locations, but have little power and seldom know much they didn't while alive. If the fate of the spirits depends on the living remembering them they are likely to be fairly interested in the living world.
The soul is recycled, split among many new lives. Typically a soul is divided among the physical decendents of the person or those who share in a ritual consumption of his body. This largely prevents contact with the dead, but may allow some of your knowledge and personality to continue, and supports many of the same advantages and disadvantages as reincarnation or possession by the spirits of the dead.
The soul is given another life. It may be reincarnated in the mortal world, alternate lives back and forth between this world and another world, or perhaps wait for a time in some other sort of afterlife before reincarnated. Waiting spirits can usually be contacted, already reincarnated spirits sometimes can be contacted but with limits - it may damage their current body, or be possible only while they are dreaming. Spirits generally have no additional powers or knowledge. Indeed they often forget most of what they knew, but some information and personality can be carried between lives.
The dead go to an afterlife detached from, and somewhat different than, the living world. Sometimes but not always there are different grades of afterlives, in which case there is probably a judging power that makes the assignment. In some afterlives the dead may gain considerable power and knowledge, in others they may lose all memories and will. Access to the dead may require negotiations with the judging power, and may vary depending on which afterlife the soul is experiencing. Souls in absolute paradise aren't likely to want to return to communicate with mortal magicians, while those suffering eternal torment may not be permitted even that moment of respite. There are probably divinations which reveal which afterlife a soul went to, and which one you will go to if you die now.
There is a choice. Either the dead soul or some judging power selects between several options. For example the virtuous go to an afterlife in paradise, mediocre souls are reincarnated to try again, and the worse sinners are utterly destroyed. This provides pretty much the same features as the multiple possible afterlives.
There is a supernatural record of every life. Regardless of the fate of the soul, information remains accessable through the record. Access to the record allows effects very like reincarnation, and multiple individuals can effectively 'reincarnate' the same memories and personalities. Shades of the dead can be called up from the record without the ethical concerns of summoning actual souls, though as copies they won't know anything they didn't in life or have memories of what happened after death, including on prior summonings. This is popular in traditions that have interaction with the dead but maintain something else happens to actual souls - such as recent Western occultists who don't wish to give up hope of the Christian paradise entirely.
Is a specific instance of Unusual Background. You can remember skills learned in a past life. These skills must be purchased normally, the Reawakened advantage simply allows you to have them without having learned them in your current life, and is a good excuse for ignoring the age limits on points in skills. This does not include memories of the details of the past life.