The quest "The Silent One" now has a followup (if you free the girl). The quest is called "Silence Broken". Once you crash Lady Vengeance in Arx, you will hear about a girl running from the carnage in the harbour, and you will find her to the north. There seem to be a few different ways to free her from the demon, I told it to possess me instead and then had my team kill me to stop him. He then summons some minions (which can be a bit nasty), though they can be completely ignored since they despawn when he dies. The reward that I got was 8 source orbs from the girl (and vendor trash from the demon). She then runs off to find her cat.