1) you'll get a message telling you when you can appoint a new prophet. If I recall correctly, it is about 6 turns after the Last one died.
2) Nope - dead is dead. The description of the mummy-creating spell (Ritual of rebirth, I think) made me think it might 'resurrect' a dead hero of yours (hero meaning someone who was in the Hall of Fame) as a mummy, but I haven't tried it myself yet.
3) Some nations have more than one national hero. There is probably a list of the heros for each nation around, if you look at sites like Sunray_be's or Arryn's.
Edit: Dang, pipped to the post by a fish.
[ March 22, 2004, 13:35: Message edited by: GavinWheeler ]