[Hasbeen]

It is possible to back out, but before he does that, he should call his recruiter and tell him of the situation..... If he is still desiring to be a Marine, then the DEP contract can be renegotiated, to reflect his later graduation date and this is definately a more positive reflection on your boyfriend. His recruiter would rather do this than suffer a DEP loss for whatever reason.

As a last resort, he can back out of the DEP contract (but if he really wants to be a Marine, why would he, take option A!) He should expect a great deal of objection, but he can do it.