Funnily enough, the fan consensus seems to be that decapitating a shipgirl doesn't kill her.
As long as she technically hasn't sunk for real, and even then there's that one trick where you don't do anything for the rest of an event to save a ship.
In things shipgirls are no longer allowed shipgirls of the sane class changed body parts so easy including their heads that it had to be banned Also Shimakaze had an existencial crisis when she anoyed Akashi so much she beheaded her for that