He could maneuver the ship into a disadvantages position, and then surrender the ship to the British. Once he was a prisoner he could give them all of the information he has on hand. While I find it unlikely that the British would let him remain in command of the ship I'm fairly confident that he knows that the British aren't going to execute them. Again, this may just be my CANADA! showing.
Again, how? How can he convince a lot of normal German citizens, none of whom have the knowledge he does, that they should abandon Germany before they've even hit the figurative iceberg? We have the benefit of rational hindsight. The crews of Blucher *neigh* and Biscuit don't. Besides, an attempt to do anything that looks even remotely like he took the easy way out will besmirch him. He just got commended by Mustachio himself, and is in charge of the most advanced battleship in the Kriegsmarine. If he doesn't die in battle, or go down with the ship, there will have to be a very good reason.