Hopefully it will never come to this, but here's what I envision that looking like:
Miami would go in the North because culturally Miami is more northern. And they would still get FSU as a cross-divisional rival. This would also put all four NC schools together, making them happy (and the ACC likes to keep the NC schools happy). In fact, the only ones who would be very unhappy with this arrangement would be VT and UVA. It would kill southern recruiting, as well as damage traditional and geographic rivalries. Maybe they would throw us a bone by giving us Clemson as a cross-divisional rival. But still, it would be like playing in the old Big East again, with a couple of ACC games thrown in.