He'd have to cost Bryan the match to make it a heel turn. That does way more damage to Reigns's credibility as #1 contender than it does establishing Ziggler as a heel (and they'll eventually start cheering him again, anyway).
I think people view Ziggler like they did HBK. The...
Ziggler's gonna screw Bryan to set up their match at Mania. Frankly, though, I'd have Bryan go over Rollins and have Ziggler cost Bryan the match at Fast Lane.
Rollins cashing in and losing would be creative's way of truly letting us know they have no idea what they're doing. So that's entirely possible.
I'm just saying, to me, it makes zero sense to have Reigns lose his #1 contender spot just because the fans are upset. It enhances nobody's story...