WWE is big on giving main event wrestlers "their win back", and I could see that happening in the case of CM Punk. With Undertaker appearing on TV last night, and advertised for the London tour, it's entirely possible the Shield "attack" was just a way to keep him on TV. Given Punk's past "affiliation" with the Shield, Punk could pick up where they left off last night.
It's being thrown around that Punk may take some time off, but that was also reported of John Cena last year after Extreme Rules, and he didn't go anywhere. I believe the same will happen with regards to Punk. He may not wrestle again until Extreme Rules or even at the PPV, but as he's expected to appear next week on Raw, I could see him staying on TV and in a feud with Undertaker for as long as 'Taker chooses to appear.
After Undertaker, it's tough to say. It appears as if we're getting Ryback vs Cena at Extreme Rules, and while Punk vs. Cena with Punk the heel chasing Cena the face would make for the best possible feud for both men, WWE would be wise to hold off on that until after Payback in Chicago. Short term, if both are available, I'd have Punk take Extreme Rules off, while Undertaker teams with Kane and Bryan to battle the Shield, with some interference by Punk costing Undertaker and co. the match.
That sets up a match at Payback between Punk and Undertaker, blowing off their feud, with Punk winning. That sends us into the summer with Punk hopefully moving back into a title feud with Cena, guaranteeing us a couple months worth of great matches. If WWE wants magic in the ring, the best thing they can do is put Cena and Punk together, give them 30 minutes, and let them go.