Assuming BB applied for the 2nd Session Summer classes by the 6/11/10 registration deadline, he would need to be on campus by 7/12/10 or withdraw from scheduled courses by this date without receiving a W.
Most people feel that if BB returns it will be for the 2nd Session which starts on 7/8/10. Under this scenario 7/12/10 is the absolute drop dead date. If he intends to return, he will probably be here by the 7/08/10 date
If he waits until the fall semester, classess begin on 08/18/10 and late registration extends until 08/27/10
I believe that if he doesn't commit to enroll in the 2nd session, the coaching staff will cut bait shortly after the July 8 to 12th time frame noted above. Everything has been kept in-house and low-key to date to allow him to return to the team upon player approval. As many have noted, any return will have staff requirements as well.
I haven't looked at the K-State enrollment/registration requirements but that will have an effect on his options to transfer and play there as well.