Sting has gone on record recently saying he sorta regrets not signing with Vince. In hindsight, how bad did Vince REALLY do by guys who came in from WCW? And not just from when WCW got bought out. Think about it, people forget this moment...
Two former WCW guys both holding WWE AND World Heavyweight title. Doesn't get much bigger than that coming from the rival company just a few short years prior. Booker T also had a great run in the WWE.
Imagine the matches Vince could've put on with Sting even past his best years:
Rock vs Sting
HBK vs Sting
Undertaker vs Sting
Sting vs Cena
Sting vs Edge
Sting vs HHH

God damn...
It's unfortunate that he never signed with them, but I never thought for a minute that Sting would've been made a mid card jobber. Undertaker vs Sting at Mania might've been one of the dopest angles ever going into Mania.