Well, Ric Flair's last match is going to be at Wrestlemania, and if he isn't losing to Triple H like he wanted to, then who is he going to lose to? He won't drop the career match to say, Mark Henry or anything. The only other possibility would be if he lost to HBK. I'd bet that Triple H would want to put Flair out of commission more than have the main event again, but who knows, maybe he'll pull the right strings and end up doing double time just to get what he wants - hopefully he doesn't, though. I don't want Batista/Orton, but I sure as hell don't want Triple H/Flair AND Triple H/Orton.
EDIT: The more and more I think about it, the more it makes sense to give the Undertaker the Royal Rumble win. They clearly know what they're doing at Wrestlemania with the World Heavyweight Title, and they aren't probably sure yet what they want to do for the WWE title, so having Undertaker win the rumble gives the WWE nearly an extra month to figure out what they're doing on Raw, as opposed to rushing a solution in January and then spending the next month on Smackdown just prolonging the inevitable Undertaker win at the Elimination Chamber.
If that's the case, and its a predominantly Raw chamber with 100% assurance that a face wins, the only possible winners can be Batista, Hardy, HBK, or Triple H. Batista would have to jump ship, and I don't think they'll do that anymore since Cena will be returning after Wrestlemania and that would over-pack Raw. HHH, I still think he's beating Flair, not Orton, so he's out. HBK is tricky...he's already had his Orton feud, he doesn't want a title run, and he's in a feud with Kennedy, but really, the two of them aren't going to have a singles match at Wrestlemania most likely, but HBK still needs to be involved in some way, so unless he was chosen as the one to beat Flair (which would leave HHH open for Orton, ugh) then I don't know how they'll utilize HBK....maybe in a tag team match of some sort. This leaves Hardy, who has been just reaping the benefits of his upward mobility lately (no pun intended) and could very well come out on top of this one to challenge Orton at Wrestlemania. Overall, for Hardy's chances, I think it depends on his match at the Royal Rumble, so hopefully he has a great one that impresses them enough, as he'd be my favorite option since we've seen everything else enough already.