The “extended coverage” that they add to coverage A (that extra 20% or whatever), do you get that if you are buying a new house or only if you are rebuilding?
You should get it, either way. It is a better strategy to reach an agreement with the insurance company about how much it will pay to replace the destroyed house before discussing how you propose to replace your home. However, you will only get it IF you establish that the cost to rebuild the home you lost and that you incurred, or spent that amount. You can usually only recover it if you spend it, but make sure that you have established the amount available before you buy your replacement home.