Unless it's the Sirena, in which case the ship may sink and so will your game - see the above screenshot, that's what I'm guessing happened there.
It doesn't matter if you assign an officer or not, boarding the Sirena (or the third ship if you're defending Bridgetown) will hang the game; you have to sink the ship by cannon fire. This was already known. But if @vince villodres did sink the Sirena by shooting it to bits and the game got stuck anyway, we have a new problem. Hence my question. 

