I decided on a whim, what if I keep avoiding Furrante? It seems this wasn't expected behavior, and I can see why, considering how he homes in on you at first opportunity. Anyway...
I killed Benweth without the quest, but the quest completed, and it said Furrante had given it to me, even though I'd never met him. Out on the world map, his ship is still stalking mine and if I let him catch me, he asks me to kill Ben. I reported to him in Dunnage just now, but his boat is still haunting mine.
So anyway, grats Fireballs, you confused the game, woohoo. Yeah no, I didn't make this post only because of that. It's because Maia actually reacts to something Serafen says about Benweth in that first meeting with Furrante. And we all know we have to get to Neketaka to get Maia, so even though you're not supposed to be able to avoid that immediate post-Maje meeting with Furrante, there's at least one interaction that assumes you do so.
I intend to let Furrante chase me across the Deadfire and eventually bring him to Ukaizo with me.
Update: Furrante has now been hanged, but that's not stopping him. Maybe if I let him catch up, he'll ask me to reload and reconsider my decision?
P.S. How I keep avoiding him: