According to Greg Flugaur, this is the order FOX prefers expansion candidates:
1. Notre Dame
2. North Carolina
3. Florida State
4. Miami
If Florida State became available, they would be #19. That means #20 goes to Notre Dame if ND wanted it. If not, UNC would have next selection, and if UNC didn't want it, it would go to Miami.
I don't think there is any scenario where the B1G would have to go any further down the list than that.
Notre Dame could insist on independence
UNC could go with the SEC (and Flugaur insists that the current UNC administration prefers the SEC)
But I don't see Miami in any way, shape or form turning down a B1G invite.
His sources also say that FSU wants in the B1G.
So the likely outcome here is FSU #19 and then either Notre Dame joins at #20 or Miami does, as UNC appears set on the SEC.