Why not fire the torpedoes?
I've been thinking about this for quite some time - but without getting it done...
With the Boat lying on the bottom, some 270 meters down, could the crew not have fired the torpedoes? They were not inside the boat’s pressure hull, so no risk of damaging that.
The warheads could probably have been defused, so they would not have the risk of an explosion, damaging the boat.
With four in the front tubes and two aft, the boat would have become some nine tons lighter. She would have gone off the bottom of the sea like a champagne cork, so if the Royal Navy were still there, waiting for her, they could only have gotten her with anti-aircraft guns 😀