They weren't. This has been asked before, or a question very much like it. It was never "a thing" for a Captain to deliberately go down with his ship, and they were never expected to. Some did, but there are very few cases. Admiral Senes, and all of his officers, went down on the French cruiser "Leon Gambetta", but whether it was a form of "ritual suicide" as it were, or that all the officers were simply lost is hard to say. (Incidentally, it was sunk by Captain von Trapp, of "The Sound of Music" fame.) The Master of the "Laconia" deliberately stayed in his cabin when she was torpedoed, but he had also been Master of the "Lancastria" when she was sunk in 1940, with the greatest loss of life of any British vessel, so was obviously feeling traumatised by that earlier event. However, the answer is, as I've said, that it was never an expectation.