You'll never get the money but at least you get rid of him.This is why it's important to inspect every unit before purchase (including physical inspection, payment history, lease terms, etc.) and why you should have a reserve.

But... if you are concerned about her ‘well being’ and she has to sell, wouldn’t you rather she sold to you instead of someone else?

(not an excuse, but perhaps an explanation)They may very well be bitter.

The previous owner still has all their stuff in there but they are not physically living there.

In the plumber's defense, it could well be the foundation for this addition was not done properly. 

If they continue to pay their rent even in a recession, the state of the larger economy doesn't really matter to your financial well being.

It will probably crack again, but this might well be a solution you can live with for a number of years before having to address is again.

It is a good idea to:Spur them into action to redeem; and/orLegally gain official possession of the property in case there might ever be some dispute about whether you were physically in exclusive and continuous possession.

In other words, a digital copy of a physical original is generally enforceable, but not 100% bulletproof.That said, I’d suggest holding onto the physical originals that you already have. 

I successfully eliminated all types of crawling pests larger than an ant from a duplex we own by physically sealing all holes that I found with caulk or even that nasty yellow gap filler stuff for larger areas.