It's not just losing the work force, but stores will have less income and may have to lay off American workers and so on.

They could rent out an investment property to a regular tenant but they wouldn't be guaranteed 100% vacancy and a responsible party to look after the property. 

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The Bigger Pockets book store if full of great books: https://www.biggerpockets.com/store

Currently looking for CARPENTERS, ELECTRICIANS, PLUMBERS, ROOFERS, DEMOLITION MEN, WROUGHT IRON WELDERS, TUCK POINTING / SIDING, PAINTERS, GRANITE, CONCRETE, IN GROUND POOL PERSON, CLEANING/DETAILING PERSON, ROOFERS (regular and wood) and possibly some others I'm missing.  

@Brad Fausett Well, I think regular property inspections and getting a lawyer on the case as soon as issues emerged might have helped the situation.

This is an easy answer for me, since in a way, I start over on a regular basis.If I had nothing, and this includes no knowledge, I would start by:1 - learning: A - How money works, B - How to analyze markets (as in zipcodes), and how to then find Micro-Markets2 - Then, I would develop a plan of investing based on the two Core Knowledge Bases above.3 - Next, I find my money, as in cash partners and credit partners, all to be implemented on a project by project basis.4 - Now, I camp out in the market(s) I found in step 1, and invest following the plan I developed in Step 2

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You can set up workflows so that when an email comes in you can send an auto reply and it can store all your conversations, track the progress of the lead, issue reminders, etc.  

I would have visited the apartment building more regularly and kept a list of which units were being repaired and re-rented.