Why would he return as a face and lose all the heat he had with Heyman and Taker.
Because that feud is over. And it's not like he was drawing nuclear heat or anything, they were cheering him throughout his entire heel run. (If anything, maybe he'll come back and say that hearing his name chanted along with Undertaker's name - one of the most respected men in WWE - the week after WM made him realize he has all the respect from the people he needs.)
He has no real motivation to attack Cena (a feud Vince is currently sick of and so am I) and help out Ryback. He and Ryback are kayfabe enemies, remember.
As for how Punk and Heyman split, Punk will likely return to a huge ovation but he'll still show loyalty to Heyman until problems arise with either Lesnar or Axel. That's the obvious way to go and watching the Highlight Reel segment right now on Raw, it's already sparked an idea on how it'll go down. Punk will return to face Jericho at Payback and then Curtis Axel will come in and interfere on Punk's behalf. This will piss Punk off, as he will really wonder why he needs a "rookie" to help The Best In The World to win a match. This leads to a conflict between the two that Heyman tries to control but can't, and for some reason, it leads to Heyman choosing Axel as the future instead of Punk.