I'm okay with coaches having "the talk" and telling the over-recruited players that a transfer would be their best opportunity to see the field. While its talked about alot, I can't think of any examples where a coach actually didn't renew a scholarship for players that didn't want to leave - seems that they'd be crucified on the recruiting trail. It's usually masked by dismissal for grade or disciplinary issues, which may or may not be trumped up, I guess. There's also the movie option of the coach making life a living hell for players that refuse to leave.
If offerring a 4-year scholarship, I'd expect a 4-year committment from the player in return (or at least until graduation or turning pro). However, there must be some sort of clause in there requiring that the player remain in good academic standing. That would give each side an out.