In our area septic lines can cost you $10K real quick if blocked by roots or collapsing.

The collapse and "L" shape recover in oil, Bakersfield has had less of a recovery than most other areas in California. 

I approved the expense - in my mind picturing broken pipes and the ceiling collapsing if not done timely.I just saw the description of work today on PM's website:  "New p-trap, sheetrock, caulking"So, did I get ripped off, & can I or should I challenge the PM on the expense?

If left unchecked the wall could eventually collapse inward with undesirable to catastrophic results.It may be possible to brace the existing wall to halt movement and/or support the building to allow that section of the foundation to be repaired/replaced.  

Even during the housing collapse where we saw 25% drops in Montgomery County, 50% drops in PG County...certain neighborhoods in DC did not go down at all and continued to rise.

If catastrophic(financial collapse) you will be liquidated and could be on the hook, although unlikely. 

@Jonathan Twombly What's a newbie like us to do pending such a collapse.

Many do not predict another 07-08 collapse as that was the perfect storm of several causes.

IMO, buy and hold reduces a lot of those issues as market moves don't tend to affect rent rates as much (outside of a larger area economy collapse). 

Also, these properties typically need upgrading/repairs that when combined with the purchase price will bring your total "in" cost much higher.Some investors have been successful finding properties that meet the 2% criteria during certain economic collapses, such as outlying areas of Phoenix and Las Vegas in 2009-2010.