I'm not sure if the new AAC members like UAB would abruptly leave since they just became members of that conference. Plus, I am not sure about the legalities of just joining a conference and then leaving suddenly. It would be interesting to see who would be the addition to the Sun Belt West if Texas State were to leave, but I also think we would have limited options.
Ideally, we would love to entertain the thought of programs like Memphis and SMU, but they are both waiting for that phone call from a P5. And I don't think the Sun Belt would be their ideal choice. One school that I think would geographically would be a decent fit that no one has really mentioned would be Tulsa. They're in Southern Oklahoma, and I think they're a name that people are familiar with. I would see some issues with them (small private school and no baseball team) that the conference would have to discuss, but the only other option out west that I see is maybe an FCS call-up like Missouri State.
I feel like Louisiana Tech, WKU, and MT have publicly burned bridges with the Sun Belt that may cause havoc if they were entertained to join. I could be wrong, but it will be an interesting list of options to bring into the western division.