Sting is getting on in years he could either:
A. Retired for good.
B. Has signed to WWE contract.
If he does go to the WWE that would be epic knowing the history of Sting never going to WWE when WCW was bought plus he could become a hall of famer and a Sting vs Undertaker match would be pretty epic too if creative went that route as Sting is an icon.
Alternatively, he shows up when Hogan makes another appearance on TNA, in black and white face paint, looking from the rafters then a baseball bat and scorpion death drop on all of Immortal.