Something this small could simply be floated to the surface. With big things there no way that can be done. Still difficult af but possible, don't know if things like that already exist.
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.