I suppose with Punk all heel'd-up, Orton would be the natural second choice for a Cell opponent with Cena out of the picture. However, I believe Orton is off to shoot a movie soon. I assume that's also the reason why he was put over Ziggler on Sunday; at least, I can't think of any other purpose for that booking.
Chances are Cena will work Hell in the Cell regardless of the elbow. As much as I don't really care to see Punk/Cena go on too much longer, there's not really enough time to throw together a decent fallback option.