What is the "fair market value" of a home in a neighborhood that will not be rebuilt?
It would be cheaper to just pay off what remains of the mortgages. Nobody is guaranteed a return on a home destroyed but with no insurance.
The same with the Northridge earthquake. The insurance company started with about 17K, and ended up with 95K on my triplex (a place I knew was poorly built in places, and really, really needed quake insurance), and the pad became much better than it had before. (Pity the softwall garage didn't collapse. I am having to pay a fair amount now to avoid that collapsing in the next one, given that the deductibles are so high.) There is safety in numbers methinks.
"Will not be rebuilt" has a built in assumption -- that the land will be converted to a wetland. Which means that some government is seizing it pursuant to the eminent domain process.
The government will hire an appraiser, the property owner will hire an appraiser, and a jury will decide. A local jury.