Carrol, Kiffin, Orgeron(interim), Sark, Helton. Yeah they pretty much land on
their feet once you're head coach at USC. It's almost like someone else high up will give you a job again. Helton was a bad hire from the get but he'll probably be just fine finding another coaching job.
Stability has many forms as I mentioned. Yes you will be fired sooner at USC than BYU, but in many ways it's still a springboard to another gig somewhere else.