Well, it depends. If they want to ahve Cena play uber come from behind face, they'll ahgve booker win two in a row, go up 2-0, then ahve Cena do the "impossible" and take 3 in a row and the title.
I think Book will come out the champ in the end. Cena's going to be off filming his movie, so there's no point in giving him the belt back. When Cena comes back, I'd imagine they start mixing him into the ME scene.