The word on John Cena's injury is that he's recovering slowly from the surgery to have chips in his elbow removed. He's scheduled to be back at Raw weekly from this point on, but whether he can physically wrestle at Hell in A Cell remains to be seen. It's probably going to be a "down to the wire" decision.
One idea that was discussed at Raw this week was the idea of Cena being involved in a Punk vs. Ryback match as a referee or some other fashion.
Punk will be wrestling Ryback this weekend at the house shows in what is probably a run-through of their potential match.