I don't see taker losing again at mania. That's why they decided to not have Brock and taker fight again at mania 32 because everyone would expect Brock to win.
I don't see him losing at Mania if he's facing Sting, tbh. Because Vince will never get tired of telling everyone WWE>WCW.
If he were to face someone else, then he'd probably do the job.