Another ending I see is The Shield attacking and laying them both out. As they both recover on spaghetti legs, Cena manages to get the advantage over Ryback (perhaps he got attacked first and thus had a little more time to recover) and Cena wins. Similar ending to the Night Of Champions 2011 bout between Triple H and CM Punk (three people attacked the both of them too, ironically.) This allows Ryback to try and say that Cena only got over because of using The Shield's attack to his advantage. Of course, Cena could retort that he was attacked by the Shield as well, but Ryback is a heel and is already being whiny so he's not supposed to be the one in the right, though he'd have a valid point.
Another ending (the one I'd love the most) is for The Shield to attack but for Cena and Ryback to fight them off successfully, and when all are cleared except for the guy Ryback is taking care of, either Ryback hits the Shell Shock and then Cena quickly gets in the AA afterwards OR (my favorite) while Ryback still has the guy up in the Shell Shock position and is goose stepping around the ring, he goose steps right into an AA before he can even hit his finisher on the third Shield member. Soon as he turns around before even getting a chance to hit his finisher, Cena bends down to pick up Ryback and Ryback drops whoever he has on his shoulders and gets put in the position for the AA and loses. (In either case here, I see The Shield recovering and then laying them both out to end the PPV.)
In this case, Ryback would have a legitimate case that Cena took advantage of The Shield's attack to his advantage, and it would be a good enough reason for Ryback thinking he deserves a rematch at the next PPV.