Len Wein and Joe Staton did a mini-series where at the end Hal was offered to become the official trainer of the GLC. I'm betting he goes one better and is offered to become a Guardian and accepts. He stays on Oa since everyone on Earth thinks he's dead and rebuilds the Corps from there. But John Stewart, Kyle Rayner, Guy Gardner all are founding members of the new GLC with Alan as the trainer.
Personally, I really don't like having so many characters with the same abilities. Especially ones where they all have the most powerful weapon in the universe. By all accounts, no evil should EVER escape their sight in that case. So why can't they get rid of it?
That's why there should be only one.
