I don't know if I see a way forward.
How do you convince a fan base that you've been selling CUSA to for half a decade that all of a sudden you have to share a room with ULL and Arkansas State again?
One or two teams added to CUSA and maybe you can get by. WKU and Middle finds themselves back in the Sunbelt again and you might as well close up shop.
Don't underestimate the power of bruised egos.
Maybe you scrap it all and just start a new regional conference. One based in the South east and the other based in Texas and west of the Mississippi. But don't bring CUSA/Sunbelt branding.