At first I was gonna say yes he should come to WWE but only if he were to get a Undertaker schedule as he is a family man now plus he's pretty much done everything in TNA but thinking about it, maybe he shouldn't. I mean back in the day, hell yeah he should've come cause you had The Rock, Shawn Michaels, Stone Cold, Triple H, Taker etc. but most of them have gone now or about to leave. Those are guys who everybody wanted Sting to face, not guys like Cena & Orton although if he came now then unlike Rock & co. he would most likely beat Cena, Orton etc. I think Sting should come to WWE but for one match only with Taker and so what if he loses to Taker. Both men are pretty much in the same boat as each other and if you ask Sting, he probably respects the hell out of Taker & his streak so much that even he thinks he shouldn't break it if he were to face him. It wouldn't be like he's jobbing to Funaki.
Also Sting is legend, I believe if he came to the WWE, he wouldn't get buried. I remember seeing a video where Sting said he didn't want to come to the WWE because he saw a segment where Rock buried Booker but Booker wasn't exactly legendary back in 2001 and Rock was a bigger star than him anyway, Sting is a bigger star than Cena & Orton, so there's no way they would make him job to them unless Sting thinks it would be more better to put them over since they would benefit more from the win.