I don't see any reason Mustain would stay.
I would bet Kiffin uses his powers of his mouth and motivates most of the Trojan Jr. and Sr. starters to stick around and give their all for USC.
But some guys, like Mustain, who are buried on the depth chart and could easily transfer and compete for a starting job will get the hell out of Dodge.
Even if this is all true, ESPN and the Networks will keep USC alive during every commentary, if for nothing else but to keep the west coast viewers. This "PAC-16" thing might hurt them worse than the NCAA. If they go backwards and the Conf. gets stronger it could be a while before Kiffy gets rollin (if he can even do it clean).