First - PAC12 isn't considering Craig Thompson. This is based off of one tweet by a random cougar fan who has never broken news before. It's pretty clear this is a joke
Second - even if the Pac12 did make a terrible hiring, it seems quite a leap to assume USC and Oregon would go Independent or that ND would dissolve their tenuous connection with the ACC. As any BYU fan knows, having a few solid games late in the season is a huge win for scheduling. But USC or Oregon would be much more likely to use their leverage to force a change at conference commissioner. Given the say that those programs have, if there's a bad hire (like Thompson) it's because USC was pushing for it.