I agree that he is undersized and didn't have the opportunity to show much on the court. That said, if he's even being told he'll be a late first round pick, it's tough to turn down around $1.9M (lowest first round salary) guaranteed over the next two seasons.
If he comes back and plays poorly or, God forbid, gets injured again, he'll likely never get the chance to make that kind of life changing money again. It's too bad the kids aren't allowed to come back if not drafted.