I am sorry you lost your MR in the sea. I hope some of it is salvageable, but I would say chances are slim. Salt water is very corrosive.
The thing about all these mishaps with MRs is. If you have any experience in RC model aircraft, then you know new pilots will crash their models and just accept it.
Put into perspective. Most new RC pilots will crash about a dozen planes before they are competent pilots. It is just an accepted fact. I don't think modern MRs are any exception at all, just people think these "new" machines are supposed to be safe and fool proof, they are not. You have to become a good pilot and put in your dues. And they rely on new programming and electronics that are bound to have problems. Look at NASA and the expensive hardware they blow up.
I have crashed dozens of planes and heli models over the years, almost all were my fault. I have had bad glow plugs, failed servos, bad gusts at the wrong time, a tail come off due to structural failure and once a NIMH battery fail. But most were just me being reckless and/or stupid.
Bottom line is flying RC models is a hobby that will inevitably lead to crashes and MRs are just another form of RC model crafts. Don't blame the manufacturers, we are all living on the bleeding edge here. These are just toys after all. And if they are tools, then you have to accept them as such and fly them as such, and if you are in business making money from them, accept the risks and be prepared to loose a few. It happens with expensive cameras as well, you drop them or leave them on the roof of your car and forget and you speed off, ask me about that one, I have insurance for that. It is all the cost of doing business or the cost of this wonderful hobby.