If you're stopped, you have one foot unclipped anyway (the classic "clipless moment" being when you forget to do this. Normally on about day 2 of riding clipless, when you're used enough to it not to think about it all the time but not used enough to it not to have to...). It takes a fraction of a second to unclip the other foot - I don't think it would delay me to any significant extent if I had to hop off the bike in a hurry. It becomes entirely automatic - I "unclip" even on the rare occasions I'm wearing flat shoes, now.

Pedal crank or BB snapping = monumentally unlikely. The bit on my seatpost that went was a thinnish lip at the rear of the bit the saddle sits on - poor design TBH and my existing seatposts don't have it.

If you *did* have a crank break, you'd fall off, sure, but unlikely to do serious damage. Break a wrist if you fell awkwardly, maybe, or a collarbone if you were really going and speed.