Although it is not in his contract people are already speculating on the possibility of Sting using this opportunity as a springboard to getting into the WWE ring. The huge media push for the game is of course promoting this burning question in order to raise public awareness. I think He would do it!
Sting is a classic wrestler and will take any opportunity he can to get back into being in the ring. There is nothing but age holding him back and if he feels up to getting in there, then he will be a contender again. Many older wrestling favorites are cashing in on getting back in the ring, why shouldn't he?
If he isn't asked to wrestle on the back of his appearance in the game, it will be a real missed opportunity. In face, seeing him in the game was more like a teaser, a promise of his taking part more in future, so there'll be disappointment if he doesn't. WWE know this, and they'll have counted on it. He'll wrestle, the only question is when.
He has been gone from the ring for a very long time and I don't think he will come back for good. Him appearing in a video game is much different than actually wrestling again. I think fans will love that he is in the new 2k15, but I think that's as far as it goes.