I don't think it will happen, but there are incentives.
http://www.thepostgame.com/college-football-colorado-pac-12-big-12-expansion
The Pac-12 Network is an epic failure. Counting third-tier TV rights, Pac-12 teams will earn less per year than any other Power-5 conference, and that gap will only grow wider with the ACC scheduled to launch its own network (bankrolled by ESPN) and the Big 12 next in line if the expansion process goes well.
Pac-12 does not have an exit fee for members to leave the conference, although it does have a television grant of rights for all existing members through August 2024, meaning anybody leaving would have to forfeit their TV rights money until then. But like all contracts, both parties may negotiate their way out of them.