I think the one thing that could pull Punk back for a while would be the promise of a WM main event.

I also think that if the Reigns thing doesn't work out and the belt was still on Brock, (And I am in no way saying that it won't work out. Just a hypothetical.) Punk may be one of the few guys on the roster other than DBry, whom the fans would get behind and believe could take out Brock the Monster.

Long shots all. I understand that Mania is forever and a day a way. DBry will apparently be back, Reigns may well work out and keep improving, they may start booking Ambrose like Austin (ah to dream.), etc.

But if Vince were to offer Punk the Main Event at Mania against Brock, do you think that's the one carrot that might pull him back? Would Vince even consider something like that?

Do Punk threads still generate clicks?
​Someone was actually pointing out in one of the other Punk threads that Vince playing the HHH role in 2011 in that feud would have been spectacular.  "You don't mind if I call you Phil, do you?"  And you goddamn well know that Vince wouldn't have put himself over in that situation.  
As for now, anything is possible.  I stand by my assertion that Vince probably has a literal dump truck full of $100 bills ready to drive up to Punk's front door in Chicago should anything ever happen to Cena.  They may be on bad terms now, but time and money heal all wounds with Vince.  ​