Drowning a bike in seawater is not like drowning it in fresh.
Seawater is terribly corrosive, and even if you get the water component out of the system, you're almost certain to have salt remaining. Anytime the system gets wet, the salt goes back into solution and continues its work. Galvanic reactions are greatly accelerated in salt water, too. Our bikes are full of dissimilar metal connections, normally they're not a problem. Add seawater and your engine becomes a sacrificial anode...
Unfortunately, any bike that spent time underwater is likely a write off.