I'd be more concerned about water moccasins under the seat.
Seriously, a car that's been underwater for days will never be the same again. Mostly it's all those electrical connections and sensors. Even if you manage to clean it up and get that fishy smell out, things will just stop working at times, from windows and door locks to the engine. It is possible to WD-40 every single connector and plug, but even then you will have strange problems. And that fishy smell always comes back in the summer.