Maybe I'm naive, but I'm not sure why everybody thinks it's such a lock that Cena wins. I know he's Super Cena but with everything WWE has done right this spring (From Bryan and the Shield to Ziggler/Big E/AJ and the amazing talent ready to come in from NXT like Bray Wyatt), I find it very hard to believe that they will just crap the bed with Ryback. They either create a new superstar by giving him the title or destroy him for a long, long time by having him come out the loser AGAIN. Considering that having him win really has no affect on the teflon John Cena, I can't fathom why they wouldn't do it.
Think about if he were to beat Cena for the title, then try to finish him off on Raw after he's done talking about "overcoming" on Raw the next night. Send in Daniel Bryan to make the save, getting the biggest pop of the year, and you have two new superstars set to have an amazing summer feud for the title. Give Cena 3 months off to recover from injuries sustained at Payback and you'll even have a fresh John Cena to come back to later (not to mention the real guy John Cena could use a break). His return might even earn him some cheers from non-children if he waits long enough.
This is a huge opportunity to create a superstar without upsetting the apple cart (Cena). I can't fathom why they wouldn't do it.