If GCU and NMSU leave the WAC, I could see the Big Sky trying to move Sacramento State and Northern Colorado giving them football-only membership. The WAC skates by at the bare minimum for four more years:

Seattle/Sacramento State
Utah Valley/Northern Colorado
Cal Baptist/CSU Bakersfield
UTRGV/UMKC

Other than the two schools in the Central Time Zone, travel in the WAC would actually be about the same as the Big Sky.

If UMKC walks, the WAC takes Southern Utah, putting the Big Sky at 8 members. If UTRGV walks, the WAC takes Northern Arizona and the Big Sky takes Azusa Pacific. Once APU transitions, they could move to the WAC and it's possible the Big Sky could get a school back.