The thing is burning, and if they couldn't get it out, then leaving is the only option.That's part of the game. They won't stick to a definition.
Yeah, the ship being abandoned by it's captain and all hands makes it salvage. That's not done unless you are screwed.
It'd be better environmentally if it burned all the oil off while afloat, but I doubt the hull can withstand that heat long enough for it to happen.
A tanker spill to add to the mix in the area is a very bad thing, with that many munitions fly around. Hard to do oil abatement procedures while under constant drone/anti-ship attack.