small river
Once you clear the 14/14 pirates, if your friend was the one who boarded the ship leaves, the ship Jacques is on will start sinking.
I was talking to him when i started taking on water. Wanted to read the dialogue noticed i was taking damage.
I stopped talking to him, didn't finish the quest, and was sinking with the ship. So not only did i not complete the quest, but i couldn't swim to the surface and get on my own ship. Not sure if it's intended that ships with critical NPCs are supposed to sink immediately.
Edit: He didn't know Jacques was in the lower deck, and didn't talk to him either despite needing the quest. So he just kinda auto pilot'd the sequence of leaving the enemy ship.