The captain only has to go down with the ship if there are still people on board by the time the bridge begins flooding.

Eh, incorrect. A captain's job when a ship is sinking is a couple of things. The first and most important job is getting everyone to safety calmly. Now let's say you get everyone to safety. THEN, you can leave. But if you fail to save everyone and have a few hundred or so left on board, you have 3 options. 1: Go down with the ship. 2: Jump into a lifeboat and leave everyone else on board. This is a bad choice because you are forever going to look like a coward, who doesn't save lives and saves himself, not everyone else. Or, 3: Tell everyone to find a floatable device or lifebelt, and tell them to jump and then tell them good luck. Also, tell them the truth by this point. Then, when everyone jumps, you can jump too or go down with the ship.