Why would the ACC fall apart? UNC, Duke, Wake, UVa, and NC State will never leave each other, and Georgia Tech, Maryland, BC, and Miami are not likely to headed anywhere. That's nine teams, there will always be an ACC.
If the ACC comes calling, SU will either go there or the Big Ten. Not even a question. If the Big East joins with the Big 12 remnants, it will be the Big East remnants doing so. Cincinnati, Louisville, South Florida, West Virginia, Kansas, Kansas State, Iowa State, TCU, and some add-ons like maybe Houston, SMU, etc.
Pack your bags, abandon ship. Death to the Big East.