I feel it is important to allow the dead to have some influence on the game.
For one, it makes for all sorts of interesting abilities. Call of the Dead is a good example of this. It allows the dead to get information to the living, and also allow them to tell the user things they have noticed, which can help the living immensely.
It also helps keep dead players engaged in the game, which stops them from just leaving.
When I was thinking about the Priest Rework in the Master Rework of Doom, I realized one problem in giving all the interaction to a single class. If that class dies or is converted, you have cut off all access they have to the living. If you give them power after death, they can still be converted, and we don’t want unconvertibles.
So I feel we should have many classes that can interact with the dead in small ways, probably including the Priest. But we can’t let it all rely on one class, so we should have a host of minor abilities.
This could come in the form of the classes for living players, or even possibly very minor powers for dead players.