I don't see any kind of scenario that would have Punk win and retain his title at the Royal Rumble. In fact, I'm going to go as far as to say that Rock is the one behind The Shield. Shield keeping the title on Punk over the last few months, so Rock could face him. This way, Rock can be a heel, and he can garner all the heel heat that's needed. And of course, Superman himself, Cena, can be the one to take him down at Wrestlemania.
many would think it sucks, but honestly, it's a very realistic angle that would also make a lot of sense. Cena beats Rock. Rock goes away. WWE goes on with life as usual. Probably bring Rock in at WM 30 for one more match with Cena. yada yada yada.