Yeah, no fight needed. He just need to tell Halfdan the story and Im sure the latter won't risk bringing the wrath of Thorkell because of a slave. He will probably just demand payment and let him go.
Isnt his gang vice-president the one who likes her and is going to ask her out? I mean he even threatened Fable to not touch her. Imagine what he would do to this minion when he finds out he wants to pimp her out.