It's hard to see them as anything but the most fragile, if for no reason other than the fact that they're the youngest. This meme of 4 superconferences is more likely to involve the dissolution of the Big 12 than the ACC (ACC, Big 10, PAC-12, and SEC are the 4 BCS conferences with the greatest longevity). If you removed Texas, Oklahoma, and, to a lesser extent, Oklahoma State from the Big 12 (and placed them in, say, the PAC-12), Kansas would probably be the only remaining school that would land on their feet, so to speak. Baylor, Texas Tech, Iowa State, Kansas State, TCU would all likely be dead in the water. WVU would be sweating some serious bullets--they could easily end up in that group of schools with no conference.

Something to keep in mind in all this is that most people instantly attach 16 teams per conference to the 4-superconference idea because they're simpletons who can only think in powers of 2. However, there's nothing that would really FORCE such a requirement. One conference may have 16 teams, another 14, yet another 20. In fact, when you consider the both the current and historical landscape of college football, it should actually seem more likely than not that the top 4 conferences will not all have the same number of members.