The most interesting possibility is that Conan will jump to CBS and take over Letterman’s show. There’s some precedence for that - after all, he followed Letterman on NBC. Leno’s not going anywhere, so if Conan wants a shot at 11:30 he has to move to another network. I think he has about 2 years left on his contract at NBC, and I think Letterman’s contract is up at about the same time.
Letterman is approaching 60, he’s had heart trouble, and he’s got a new baby. His ratings are down, and he looks tired. It’s not inconceivable that he’ll want to retire sometime soon. And when he does, the obvious replacement is Conan O’Brien. And I think he’d kick Leno’s ass.
The biggest problem for O’Brien would be the loss of all his current gags and skits. Most importantly, the potential loss of Robert Smigel, who’s always been intimately connected with NBC (Saturday Night Live in particular).
Still, if I were a betting person I’d say it’s better than 50-50 that within 10 years Conan will be on CBS.