While I'm not saying that Oakland will overtake San Francisco anytime soon, I believe the population growth is big enough where Oakland is also seeing a portion of this growth.I am long bullish on Oakland and barring some crazy event where tech collapse and all tech professionals move out of the Bay Area, I think this will become a prime location.Feel free to PM me if you like to chat.

How quickly could the population of 25,000 collapse down to 15,000 or say 10,000?

Then a collapse will begin with widespread layoffs which will in turn affect housing.

Rents in many markets increased during the housing collapse.

Other than that, you are looking for signs of a leaking roof, or structural issues (bowing roofs, walls, collapsed foundation walls etc.)

At a 10% to 15% deductible, my buildings would have to sustain substantial damage or completely collapse before I saw anything from the insurance company. 

I think most people did not know the tulip market collapsed right after futures were introduced.  

You bring up a good point that in real downturns like '07-'09, a lot of things collapsed including the closing of lines of credit.

What it refers to is the collapse of underground mines and the hour glass effect it causes on the surface.

It will take only a few quarter point rise in the prime rate, or one major Fund collapse, and I can see it all coming down.