We take him into the sewers and some bandits attack us, so the mage, who Sister Petrice calls Ketojaan for some reason, crushes their heads. Anyway, we get out of the sewers and I get attacked by the Qunari because the mage no longer has a role in their society and they want to kill him, so I kill them and then once I set the mage free he sets himself on fire because it's what the Qun calls for.
We head back to the warehouse where we met the chantry sister to find her furiously destroying evidence like she's a one-woman Nixon administration.
At this point, you're given the opportunity to say you should kill her. (Note: You can't kill her.)
So she walks away and I get like one gold and +5 rivalry from aveline for letting a wrongdoer go free. If I had said I wanted to kill her I would have gotten zero gold and probably +5 rivalry from Aveline anyway for threatening a member of the chantry.