Well, it may be a long shot, but I think that after being permanantly exiled and hunted by Azula, Zuko will have a revelation, and realize that it is his father, and not Aang that needs to be stopped.?? He and Aang will team up and learn to bend better, eventually Zuko will become a powerful ally in the final fight.?? In which Iroh will either die for Zuko or Aang, or go nuts and have a fire freak-out.

Ah dude comon we've had a bunch of these. I mean the Who do you think will teach aang firebending??? thread thingie is like two spaces away from this.