It is too easy to flatly declare that breaking off would or would not violate anti-trust laws. The reality is a lot more complicated than that.
The 1984 case between Oklahoma and the NCAA continues to have ramifications here. There, the court acknowledged that in college athletics you have to be able to make arrangements that in other contexts would be unlawful as anti-competitive just because of the nature of the beast. But it also acknowledged that you can only take this so far.
How an anti-trust challenge would turn out is far from a settled question (especially since we don't yet know what allegedly anti-competitive conduct they would be trying to challenge).