I think it would be stupid to use the deckgun and flak. If you must surface to escape sinking, then you must. But try to leave it at escaping, and not show them where you are. If there is any chance that the trawlers and the destroyer is in the fog of war, un aware of you when you surface, then leave them there. And go home licking your wounds.
But if they clearly know where you are, then I suppose it's a question of sinking, or likely sinking. Not much to loose. Your description doesn't exactly tell which situation applies at the moment you surface.
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