Being such a big Sting fan this is a delicate situation for me. Having Sting lose to The Undertaker at Wrestlemania is NOT an option. Sting's whole fear of going to The WWE was that they'd make him look inferior to their product. Taker beating Sting at Mania would do just that. Sting would take it as an insult and he would either become disgruntled or just plain wouldn't sign a contract if the story was proposed in advance.
Honestly, almost nothing makes sense. Sting going after Cena? Why? They're both super heroes. Sting attacking the Corre or helping Taker? Why? There is no legit reason for Sting to care. Since Sting is known for being Anti-WWE him showing up to do something period doesn't even make any sense at all. Almost anything would feel awkward being a long time follower of his.
Here's my only loophole to possibly make something work. Take instances from the past, unfinished storylines, and have Vince start putting the pieces together. White paint was found on the exploding limo. Maybe a piece of trenchcoat was on the piece of stage equipment that almost landed on Vince (if i remember that incident correctly). Have him gradually come across clues until something new happens and a shadow is seen in the rafters. Vince figures it out and goes on a quest to hunt down Sting. When he finally finds him he realizes he can't do anything because hes not under contract and refuses to sign one. Vince either tricks or forces Sting to sign a contract and he becomes Vince's newest pet that he wants to embarrass. But it doesn't work. Sting keeps overcoming any odds thrown at him. Faces from the backstage area, mainly John Cena, would do anything they could to help protect Sting since he was their childhood idol.
Go anywhere you want from there. I can't settle on one idea after that. Sting has the mega rub from Cena which also gives him some back up to lighten his workload. Vince could throw anyone he wanted at Sting, even eventually The Undertaker. From there the feud could take on a life of it's own. I think that could be a likely culmination but I'd rather have the Vince feud last quite awhile. Sting could bring in demons from Vinces past for one shot deals. Wrestlers that arent receiving medical help who are in rather bad shape, wrestlers that never got their shot because they didn't have the right look, etc. Play majorly off of the reasons why Sting didn't want any part of The WWE.
I'd love to see Sting in WWE, but I just dont trust the writers. Do something like I'm proposing and I'd be more than thrilled. But honestly, with their past track record with non home grown talent, I dont give Sting a chance. We'd get three months of good storylines then an embarrassing run with Sting jobbing to youngsters. I'm probably the only person here that wants him to stay in TNA.