That's true, but if he's not signed this summer than next year he has the option of playing at Michigan one more year and becoming a UFA (and finishing his degree, which he may or may not care about). I don't think he has anything left to prove at the college level. If Adams sees it differently I disagree, but I'm sure his people know more about that than I do. If Adams wants to send him back to college simply to slide his contract a year I think that would be short sighted and foolish of him.
Also true about the players you mentioned leaving this year, but I don’t think that impacts the decision he makes next year.