I've seen multiple statements, which granted could be wrong, that 8 teams could vote to dissolve the conference.
I thought the PAC either had different rules AND/OR that once a school said "we are leaving" they were no longer allowed to vote. Since the PAC fell apart in pieces -- 2 to BiG, then Col to B12, then 2 more to BiG, then 3 to B12, then 2 to ACC .. and none were sure they were leaving until the offers came, you didn't get the single block of 8-10 schools departing at once.
The MW could've had 8 schools vote to dissolve, and then go to the PAC. Of course they'd have to be sure the PAC wouldn't screw them over....