The problem is that people cannot simply get out at scale. The homes themselves are not portable and represent a significant investment that most homeowners cannot afford to lose. An individual can sell, but that requires there being a buyer, so doesn’t actually solve the problem.
What is needed here is a government funded relocation program. The government buys houses in eligible areas at market rate (locked in at the time the program starts, as market rate should collapse to 0). Then, the government does nothing, and saves money from not needing to subsidize the insurance market, and need needing to spend as much on disaster response and relief. Given that the disaster relief savings is largely born by the federal government, this program should receive federal funding as well.
When was that house built? What should the current owners do with it? If they sell, someone else needs to buy. Someone is going to be left holding the bag for a decision made decades ago.
And our current approach already indemnifies them, because their flood insurance is provided by the federal government as no private insurer will offer it. Then, when a flood hits, we all pay for it, along with the emergency response during and after the event.