(I used to have a five-unit in Haven that I rented to college kids and by sheer luck sold it shortly before PSU started making their students live on campus, causing the value to plummet.)

During dotcom crash of 2001 I remember rental market also plummeted for 5 years. 

When they announced Chicago was eliminated, prices in the area of the proposed Olympic village plummeted and many investors were burned.  

Crypto values plummet, etc., etc. 

This means if you don't stay on top of costs your returns will plummet. 

The economy can crash and your values can plummet...

Even with buy in prices being high, good weather helps keep maintenance costs lower, there are plenty of skilled workers to get complex work done, unskilled workers are plentiful, property tax (prop 13) limits are beneficial for the long term- Due to the demand (SoCal population is definitely increasing), vacancy rates have plummeted and rents are healthy increasing. 

If you are a current owner and are currently at or near market rates and competent enough to keep up with the annual increases you are in great shape and your value and rents will only increase no matter what as supply plummets for both rentals and sales and cash flow will dictate value.

But to answer your ORIGINAL question, haha, if s*** were to hit the fan and prices plummet, I'll be waiting cash-in-hand to pick up as many deals as I can.

Simple math shows that your net worth would plummet.