As of a week or so ago, there had been no real internal talk of Sting appearing at WWE’s WrestleMania 32 but that doesn’t necessarily mean he won’t be there. There has also been no talk of Sting vs. The Undertaker happening. It appears WWE is going forward with the John Cena vs. The Undertaker match at WrestleMania 32 as it was seriously discussed it in August and then again in October.
On a related note, apparently Seth Rollins vs. Triple H was never really considered for WrestleMania 32. Word is that the match could still happen down the line when Rollins returns. No word yet on who Triple H will be facing now that The Rock is reportedly unable to wrestle due to an insurance issue with a movie he’s filming next year.