I'm not sure. If I remember correctly you slowly loose the hull integrity and if you are already damaged, the hull integrity will go a bit quicker. To be honest, I never went deep and hung out there to see the out come. I certainly will do this and find out what happens. I believe it is modelled in where if you are damaged, your crush depth is severly limited. This is a given really. I do, however, see your point on diving deep to evade and nothing happens to you. The boats can go deep but were rated by the engineers to just so far. Many going 500-600 feet deep either in control or out of control. I would be sweating the family jewels off at that depth. This reminds me of a scene in Das Boot were he takes the boat deep and all is quiet then bang, a rivet goes flying. I'm sure some Hollywood added here but all the same, could and probably did happen when going deep. I was talking to a friend who was on these boats. He said at 350 feet these boats were creaking and talking big time. Bulkhead doors would open but door inside a compartment such as crews berth and the galley would not open. That old story of a tight string on the surface that start to bend down and go slack as you go deeper is not an old story. He said you could watch the hull compress. I can only imagine how she was singing at 600 feet
I do not know it was pure guts to go that deep or the alternative of what is on the surface was worse.