Well, it looks like the Mountain West will survive with UNLV and Air Force publicly committing. My guess is the Pac-X adds Texas State and mayyyyyybe UCONN for football only. The Mountain West adds UTEP/NMSU, and/or potentially dipping into FCS.
The Sun Belt is at 14 teams so it makes sense to add one school to replace Texas State. They have their pick from Conference USA. Conference USA is currently at 10 with Missouri State and Delaware coming in next year so they don't necessarily need to add any replacements. Even with 3 defections they'd still be at 9 so they either stand still or bring up another FCS team.