WWE has had little discussion with regards Sting appearing at WWE's WrestleMania 32 but that doesn't necessarily mean he won't be there. There certainly has been no talk of Sting vs. The Undertaker, it's looking likely that it will be a fantasy match that will never happen. 

The company is going forward with the idea of John Cena vs. The Undertaker match at WrestleMania 32, it was discussed as recently as October.

In other WrestleMania news, Seth Rollins vs. Triple H was never really seriously considered for WrestleMania 32 although it could happen down the line when Rollins returns from injury. Triple H was considered to go up against The Rock but he will reportedly not be able to wrestle due to an insurance issue with a movie he's filming next year.