I dont think so because the crew compartment is/was pressurized. The real problem is that without power they likely froze to death a long time ago

If the sub is still at 1atm internal there is no issue...if the sub is at 380atm down at the Titanic then.....again nitrogen narcosis is not the issue as that 4000 tonnes per square meter of force makes it irrelevant.

Hmm I don't know if works like that when you're on a submersible. You're in a 1 atmosphere pressure.