Mysterio won't be anywhere near the main event picture for a while. WWE is using him & Sin Cara to keep momentum going in the tag team division so that's where he'll be for a while. There's talk that WWE has it planned to do Mysterio vs. Sin Cara at WrestleMania after their team breaks up, so Mysterio's attention is focused on other things.
As for Punk "going after" Cena, it just doesn't hold up. After all, Punk's reasoning for not accepting Cena's challenges for HIAC, prompting the latest angle that's taken place on Raw the past several weeks, has been because he's frequently bested Cena. Going after him if he gets past Ryback sort of renders everything they've done with Punk over the past several weeks kind of a waste of time.
Cena's injured elbow puts in doubt exactly what WWE will or can do with John Cena for the future. It's true that Cena looks good, he didn't have any sort of bandage or anything on his elbow last night but that doesn't mean that he's still anywhere close to 100%. The WWE might just give Cena some extended time off to make sure that his elbow is completely healed but to also rest up. According to reports, Cena's pretty banged up right now so time off could be what's best. WWE wants Cena healthy for WrestleMania season so he can help deliver another massive payday.
As far as who Punk will face to help take up the rest of the year before moving onto The Rock, I'm sure WWE could probably have Punk continue his feud with Ryback for a while. There was talk of possibly doing a match at TLC featuring Mick Foley against Punk. I haven't read anything else about it in a while, but the idea of Foley & Punk in sort of a TLC grudge match could be fun. Even though everyone knows that Punk will win, that doesn't mean that there still won't be some great promo segments and that they won't deliver a great, physical brawl.
As far as Punk & The Rock goes, apparently, the top idea for Punk right now is to put him in a WWE Championship match at WrestleMania against The Undertaker. That might certainly change but, last I heard, it was said to be the most popular idea. The WWE also said to be wanting Cena vs. Rock II at WM 29 and if WWE goes the route of Punk vs. Taker for WM, all they have to do is to have Cena somehow play a role that costs Rock the WWE Championship at the Royal Rumble. After all, at WM 27, The Rock did cost John Cena the WWE Championship by planting him with the Rock Bottom, allowing Miz to get the pin. Cena could sort of return the favor by making sure Rock doesn't get the titme as a bit of payback, thus setting up a simple but always reliable reason for renewing their feud for WM 29.