I've been one that's been saying the ACC is not doomed. Can there me more shifts with losing and adding---yes; but it would be hypothetical and premature to say who would go where, given the loyalties, politics, and other uncontrolable factors that shape developments.
Suppose the B1G is motivated to reach 16 quickly; or would have to go 18 just to get the two for 16 from the ACC, assuming most or all would come from there. And, the SEC would be at it again, maybe near forced to, or opportunities for certain schools are too desirable to pass up.
Say, again hypothetically of course, after the B1G and the SEC are done extracting from the ACC, the ACC is left with eight to ten full members, some of them among the ACC's best in terms of sport's output. Rather than the B12 saying, "we'll just take a couple or so of them", it becomes time for a big package of unification.
WVU went to the B12 which gave them a very respectable home. But the ACC, B1G, and SEC, passed on WVU in their expansions, leaving WVU little options for conference prestige. Likewise, one or two ACC schools are not going to want to head to the B12 unless they have to do so to remain among the elite. As much as some dismiss it, geography is still important. Also, near and tradtional rivalries are important. Access factors for traveling fans have not gone away. But if there is a significant "group" of ACC schools that transition, establishing or retaining a divisional structure that is geographic/traditional friendly, then there is more plausibility.
The B12 can add without ACC schools, though what's out there right now that's available don't excite. Also, the ACC could lose 4 or so, and replace with schools such as UCONN and Cincy. If they had to go further, types such as Temple, Navy fb, Tulane, Rice, etc. may get considered.
The B12 is talking about an alliance. After another raid hit on the ACC, the B1G and ACC consolidate. Say the ACC has 8 left members at worst, which assembles with the B12's 10 members. As part of the deal, WVU shifts to the ATLANTIC COAST division and has 9 members. The MIDLANDS division stays with its 9. This combined 18 would certainly be overall strong in the mega-conference/playoff initiatives. It may be better than each expanding on their own.
Of the Big12/ACC consolidation: MIDLANDS DIV. - UT, TTU, TCU, BU, OU, OSU, UK, KSU, ISU
(readily made division).
Of the Big12/ACC consolidation: ATLANTIC COAST DIV.- (the remaining ACC schools) - very hypothetical example - WVU, VPI, WFU, CU, UM, FSU, GT, L'ville + Cincy (from BE) - geographically sensible
(ACC division abandons very NE presence; strong in Fla./southeast; solid Ohio Valley presence).
Hypotetically for example purposes: The B1G had prior taken - Notre Dame (FT), Pitt, Syracuse, and BC (or UCONN from BE). 18 total - geographically sensible
(The B1G gets the beloved ND as full member -- complete lock on NE).
Hypotetically for example purposes: The SEC had prior taken - UNC, NCSU, Duke, & UVA -- (got the ACC core to break but hang together). 18 total - politically & geographically sensible
(SEC gets expanded into NC & VA with desirable schools -- takes old ACC core largely unbroken (the research triangle, UNC/Duke/NCSU, being together is very important for them; drawback, 3 from NC - but one is private which gives the SEC a 2nd private.)
OK PAC12, your move.