The PAC12 needs to add teams regardless of the scenario.
If OU/UW stay, then they need a couple to get back to 12 and look respectable. No different than what the Big12 did when OuT happened - add some warm bodies.
If OU/UW leave, then they gotta try to add 4 to keep the conference alive, even though it will be severely diluted. Even more warm bodies!
If OU/UW and 4-6 others leave too, then the 2-4 left behind will essentially join the MWC, but call it the PAC12 because the brand name is bigger.
They gotta start looking around and talking to people no matter what happens. No choice. No different than what the Big12 did when OuT happened.
They would also need to tell Cal and Stanford to STFU, because if the Pac were to survive, they can't be picky about who they let in anymore. Over the last decade + Cal and Stanford rejected Pac expansions that included Boise St, SDSU, and UNLV based on academics and BYU for religious reasons. If anything, Stanford and Cal might be the biggest detriments to the Pac's survival than anything else.