If you make Vince money, then he'll be easier to forgive you. If Kurt hadn't left when he did, then a few things could have happened...
1. Angle continues to be great
Needless to say, Angle is simply one of the better overall wrestlers in the biz today. If he stayed in the WWE, he STILL would be on top of his game and STILL would be putting people over, one story at a time. It takes a special person to do that.
2. Angle would lose his smile
It's also possible that Angle would have been so burned out that he'd take a sabbatical that would have lasted maybe until this year. Many know that Angle was a machine and he was slowly breaking down. So many injuries would add up and eventually, he'd short circuit and not want to do it anymore. He was injured quite a bit and simply to put your body through that punishment would be too much for anyone, especially Angle, who wants to be at the top of his game in EVERY match.
3. Angle dies
This is a morbid thought, but with the injuries, marital problems, and drug use, it's even possible that Angle would have died eventually. It's taken out some of the best in wrestling. Hennig, Rude, Boss Man, Test, Pillman, Gurrerro, Benoit, and it could have very well caught up with Angle, too. It would have been a tragic event to say the least, but it would have been inevitable if he kept going at the pace he was and the path he was going toward.
To me, those are the 'What if's' for Angle if he would have stayed with the WWE. Either way, it may not have worked out well for the Olympic Hero.