this actually did happen
not a catastrophic failure - just a regular flat
the rider (a friend) was unaware he flatted and continued to ride - and the tire unseated
Yeah, that was the type of thing I was thinking of that would unseat a tire: rolling while fully deflated.
I've gotten a few rapid deflations from large punctures while riding clinchers, so I continue rolling straight and brake gently. That several seconds of rolling drops the tire off the rim hook, where it can still be ridden safely. Unless the tire fits really loosely (modern tires like GP5000 are tight), it's not going to come off the rim.
A rapid deflator from last October:
GP5000 vs drywall screw