I don't see this happening. I see Big Show keeping the belt. Cena wins the MITB. RR, The Rock wins the WWE title and in WWE fashion they "forget" that Cena's briefcase is only for the WHC so he cashes in against Rock and wins the WWE title. This sets up a triple threat John Cena V Punk V Rock at WM so WWE still gets Cena and Rock in the same ring together but Punk gives the WWE the ability to say that it's not a rematch and shoot down all that shit IWC will talk.
In a perfect world, the original idea would happen but we all know how WWE works. Punk is out and ratings are down so they're going to rely heavily on Cena.