After that quest, since it wouldn't allow me to kill him, I had to console myself with simply refusing his marriage proposal, banning him from my quarters, forcing him to be a crafting slave, and then banging Pierce right on the tiny ship where he couldn't avoid hearing it. Though I would have much preferred to reply to the marriage proposal (which came after the betrayal) with a conversation option of: "No I won't marry you. You. Tried. To. Kill. Me. And you insulted me while doing so, by thinking that two little strong level mobs could do it. They weren't even elites!"