How do other investors in similar situations mitigate the risk of exceeding FDIC insurance limits?  

If you get info from the previous landlord consider it a bonus, not a necessity.Remember in this business you will never eliminate risk, only mitigate it as much as possible.Good luck.P.S.Give this a read,you may find some good tips in there 5 Landlording tips from an industry PRO

Obviously, it benefits them to do so to mitigate their risk.

I'd say these risks ought to be analyzed and mitigated, and then all the factors weighed carefully.

During covid outbreak and "mass deaths" the US population still GREW.

(probably not).You might be able to mitigate some of that risk if you could meet the owner and assess their circumstances before buying the property--but even then, your assessment is likely to be pretty hit-and-miss (although some people experience significant hardship through no fault of their own, it's not uncommon for people to create a fake sob story to cover up their own negligence/incompetence...even if you could talk to the owner, how would you be able to know the difference between legitimate hardship that was no fault of their own vs. a fake sob story?) 

In case you didn't realize the automotive industry basically runs that city and it was struggling before the the COVID-19 outbreak.

As for the time window to identify another property, sorry but I say that's a novice excuse because there is a list of ways to mitigate that item, legally.

It has been our experience that such floors last as long (or longer) than cabinetry in rental units.One big advantage of running the finish floor wall-to-wall is it does a much better job of containing water spills and mitigates water that runs under the cabinets (think leaky dishwasher) from seeping under the finish floor.  

There are very extreme situations you'd encounter in order to do a double close such as original seller doesn't want a third party ( this can be mitigated with some negotiation), you don't want the original seller and end buyer to know how much you're making, and you want to loose a lot of money.