For me, it is business. At this point, we have to operate under the assumption that the current landscape of college athletics won't change in the next few years. Obviously it could, but how can predict?
With that, I think there is sufficient strength (or will be after a year or two) in the MWC to garner the NY6 bid IF you schedule well OOC. Take home, byu could help in regards to strength and NY6 bid in conference, but are not necessary as long as you schedule decent OOC.
After that, you have to wonder what would they do for TV. I imagine we would get a bump but spread over 12-14 teams, it would be negligible. Net gain financially would be minimal.
The MWC as a bball conference is perfectly fine even in our down years. Net gain of byu is almost nothing.
Conference stability? No brainer, byu is a destabilizing force and would no doubt threaten the existence of the MWC. At some point shortly after rejoing, chatter of "best of the rest" conference would start in provo.
Gain for byu? Really, only the NY6 access. There is no other benefit for them to rejoin.
End analysis: byu does nothing for the MWC and the MWC does little for byu. I vote no even if they wanted back.