They could take an loan against the unrealized gain on their asset if they'd like to continue living there. If they'd rather sell and keep the cash, that's their choice. Letting them both keep the windfall and shortchange their community doesn't make sense.
In addition, California (and I suspect other states) have a means tested property tax postponement program that allows low income homeowners to defer taxes until they move out, sell, refinance, or die as a substitute for obtaining a private loan.
In addition, California (and I suspect other states) have a means tested property tax postponement program that allows low income homeowners to defer taxes until they move out, sell, refinance, or die as a substitute for obtaining a private loan.