"Real estate values are sticky and will hold up longer than people think."

This may be true in the general case, but there is a more relevant (IMO) general case here, and that is: demand outstripping supply causes prices to ramp up steeply ... but if that condition wavers at all they will drop.

That is to say, if there is even a single marginal house for sale in the SFBA that can't clear, the whole market drops. Right now that doesn't exist. All (normal, conforming) homes in SF are clearing. If that changes - if there are even one or two marginal houses left unsold - the price plummets.