I don't know that Cena is going to win clean. I don't think even Vince would like the idea of Cena and Roman both going over at Royal Rumble because you can't coronate your chosen guy at WM if they're already the champ.
My fantasy idea is that this is playing into the Undertaker interfering in AJ/Cena to play off of Cena's new schtick where he just declares he's owed everything and Undertaker can say basically the same thing.
I'm a lot more interested in the outcome of the Rumble itself. None of the top guys are apparently even in the Rumble. Goldberg and Lesnar don't seem particularly likely to win unless its shenanigans involved like Goldberg winning and then Lesnar squashing the universal champ at Fastlane. At this point, I feel like the most sensible option is Chris Jericho to set up the obvious Jericho/KO match at WM. I guess you'd have to set up the ULTIMATE VINCE BONER MATCH if you did that though, a Triple Threat with Cena/Roman/Undertaker!