Shego, of course, would have teamed up with her immediately, glad to have an equal to be psycho with.
I think Shego would actually end up being the one responsible for bringing her down. She'd think it was great at first, sure, but if Shego actually wanted to accomplish anything evil-wise, would she really work for Drakken? Kim would be good at the darkside stuff, even better than Zorpox, and Shego would end up playing reluctant second fiddle until some combination of jealousy, resentment, hidden good streak and simple preference for their old frenemies relationship finally made her snap and team up with Ron and Wade to fix it.
Though the creative team might have considered that too thematically similar to Stop Team Go. (Also, it would further highlight the intense moral dubiousness thereof.)