Most assume that Punk will lose the belt at the Rumble to The Rock, and then Rock-Cena II will happen at WM29. However, I not only suspect (as some do) that it could end up being a triple threat involving Punk (at least people who constantly harp about Rock/Cena being 'once in a lifetime' can finally shut up about it) but that Punk may end up scoring a victory against The Rock at the Royal Rumble. And the reason it'll happen is because Cena is still in his own little 'feud' with Punk perhaps, and he will end up getting involved in the title match and accidentally costing Rock the match. Would be a huge victory for Punk, and also take everyone by surprise who just naturally assumes that Rock will be winning.
If I had to make a specific prediction, I would first say that Rock-Punk will probably be the last match on the card at the Rumble. Rock's comeback to challenge Punk makes it seem like a special enough match to put it last on the card (it wouldn't be the first time the Rumble wasn't the last match on the card.) Maybe Punk will distract Cena during the Rumble and allow someone to throw him out. And then as payback, Cena will come in during the WWE Title match and try to hit Punk (with a chair or the belt or something) and will actually end up costing The Rock the match. This will stir shit up between Rock and Cena all over again, not to mention Rock might be guaranteed another title shot. And then it'll become a triple threat match at Wrestlemania. Cena wins the title, and Punk can walk away saying that it took two huge superstars like Rock and Cena and having to wrestle them both at the same time just to beat him.
Just a small prediction that I'm making. And I do have a couple of others, of course, like believing that Ryback will win the Rumble and do so by throwing Cena out last after a big one-on-one babyface confrontation with them being the last two men in (ala Batista-Cena from the 2005 RR), which obviously isn't compatible with thinking that Punk distracting Cena will cause Cena to get thrown out. Another idea is that Ryback will win the belt tonight and keep it all the way to Wrestlemania, where he'll face Rock and Cena in a triple threat match (far fetched idea, but a possibility nonetheless.) However, going by the idea that Punk-Rock will indeed happen at the Rumble, this is my prediction on what could happen.