With the news of the four schools leaving and possibly UNLV and Air Force not far behind, the Mountain West will probably want to expand and possibly be forced to if UNLV and Air Force leave as well. These are the schools likely to receive a call from the MWC even if some aren't likely.
Tulsa, Rice, UTSA, North Texas - I doubt any of these are really going to be interested in leaving the current AAC for now the weakened MWC but the MWC will likely contact them. If the AAC loses schools as well then we can reevaluate when that happens.
UTEP and New Mexico State - These schools would accept an invite. Even a weakened MWC is probably still stronger than the current Conference USA and would reduce travel big time for both schools.
Texas State - I honestly don't know about this one. The Sun Belt appears to super happy with their current set up and they're improving on the field too. I imagine Texas State listens but don't know if they pull the trigger. Maybe if the MWC also gets other Texas schools or at least nearby schools that could sway them.
Montana and Montana State - Don't know how interested they would be in the now weakened form of the conference but it would be better money and travel would not be a huge difference. They are already traveling to California, Arizona and Colorado in the Big Sky. The Mountain West travel is very similar.
North Dakota State and South Dakota State - these are programs that from a competitive standpoint are ready. I think they have more interest than has been said. I think the bigger issue has been finding a conference that makes sense geographically. Don't know if they leave without fellow schools North Dakota and South Dakota.