I'm not sure factories closing down in the Bay Area is a big issue as there aren't a lot. The bigger issue is upper middle class and upper class people and their taxes leaving. On the other hand, the area generally (if not necessarily just SF proper) has a lot of attractions that Detroit never had. So it's reasonable to assume that housing prices could drop to a more sustainable level. Of course, one implication is that municipalities would probably have to operate on lower budgets than they do today.

In general, SF and Bay Area are not necessarily the same story. Plenty may choose to live in South Bay especially if prices drop but not in the city.