Unless something drastic happens, I don't think we'll ever see Ziggler in a main event. And I'm a huge Ziggler fan, I think he could be the next Shawn Michaels, but I don't think WWE has any confidence in him at all. I think HHH see's him as too much like HBK and thats why he'll never get behind him.
As for the Mania main event, It's either Bryan, or in a real long shot CM PUNK if this whole thing is a work (I don't think it is though).
My perfect scenario… Bryan and HHH are battling it out, HHH takes out the ref, Kane and the NAO's run down and start beating down Bryan. As HHH is about to hit Bryan with a Sledge Hammer, Glass shatters, Austin's music hits Austin stuns NAO and Kane, Stares down HHH and then backs off and as HHH turns around, flying knee, 123 Bryan wins and goes to the main event. As Bryan is celebrating, HHH is slowly getting up and Bryan looks at him, points behind him, Stunner to HHH by Austin. Crowd looses its mind, Bryan goes on to win the triple threat and the title. End Mania with thousands doing the yes chant.