A vessel's master will always leave standing orders to be followed while they're asleep. Typically these orders solve only some routine choices that were anticipated, and for anything extraordinary the master should be awoken at once and consulted.

The junior watch officer should have summoned the master long before the ship hit an iceberg, if they are inattentive (e.g. they fall asleep in the warm dark of a bridge at night) the BNWAS will alarm to try to wake them, then eventually summon senior officers (typically the master, but maybe also a chief engineer and others) to the bridge. The master is responsible for ensuring the BNWAS is operable.

It would be extremely unusual for a commercial vessel (not to mention military vessel) to allow officers to drink booze, especially enough booze to fall "asleep in a drunken stupor". Of course just because something is prohibited doesn't mean it won't happen, but now we're talking about culpability and of course you're culpable if as a foreseeable consequence of your prohibited actions bad things happen, that's negligence at best.