Makes more sense to me if sufered internal damage that would cause flooding rather than be terminated by loss of hull integrity.
From a close explosion the sub will be shaken so badly that internal tubes, equipement etc would be displaced, rupture or damage beyond repair and depending on the air/water pressure will make more/less damage.
Personally rely on hull integrity is like... if the tower was knockout due to explosion or ruders/screws lost or even a critical hit that break the sub in two parts.
Anyway its just my optinion... sinking the sub due to internal problems rather than hull integrity.
But other matter require attention that is the inrealistic repair times... 1, 2 , 7 seconds to repair a critical equipment which will/not make the sub survive is a bit odd if not a joke
