The Afterlife would be a very strange place and everyone could bring a few of his own ideas into it.
Th main Story, if you want to call it that would be that there is a supposed way back into the world of the living. If your character wants to live again or not does not matter, he gets sucked into the story either way.
Also you could chose if you want to write a freshly dead character (who would be have no idea what is going on) or a character who is long dead. A few of the key-characters would be NPCs.