There have been warbirds restored to flying condition from virtual wrecks, but they have often been original in name only, with many major components replaced. Those which have been raised from lakes, for instance, and restored, have been to static display condition only. If found in deep, cold, fresh water, the wrecks are normally well preserved by the conditions, but will still suffer metal reaction which will weaken the structure beyond safe tolerances, even if the airframe appears to be otherwise corrosion free. Sea water is a different matter altogether, and even static restoration can often be impossible. Once out of the sea, and in air, further decomposition can be rapid and, although it might be possible to limit this and prevent further decay, and even produce an outwardly 'normal' looking, restored aircraft, the load and stress bearing components wouldn't even pass a touch test, let alone any stringent safety and airworthiness checks. Bottom line is, if it's been in the sea for any length of time, possibly even days, it's unlikely to fly again.