An insurance company writes off a vehicle when it would cost THEM more money to fix than it is worth. Once the payoff is made to the owner, they take the title and sell the vehicle as salvage for whatever they can recover.
I can't imagine a transmission problem causing a 2003 RV to be scrapped. In 2003 a lot of the electronics for the engine and transmission were electronic so I can see flood waters causing a problem. Insurance companies will write off flood vehicles if they anticipate future safety problems on corroded electronic components that cannot be foreseen with a simple inspection, especially if it was salt water. As salvage of parts only, that are not electronically controlled, the price is way too high.