To the point, here is my suggestion for the main event at WM:

Rock and Cena versus CM Punk and Stone Cold
Punk and Stone Cold win, but Undertaker shows up. He knocks out CM Punk post match and celebrates with Stone Cold -- and all the legends applaud The Undertaker's official retirement

How Cena and Rock team up: Cena helps Rock after getting jumped by Punk at an earlier PPV. So they are forced to team up against Punk and anyone that the Punk chooses.

This is teased for a while until Heyman reveals that he has paid for someone to appear at WM... Stone Cold. Of course at WM Stone Cold kicks CM Punk's butt post match and refuses the "damn money"...