I have the same issue. Although closing PoE and Steam and restarting did not fix my issue.
I''ve tried to upload my output_log, but the attach file in the uploader fails.
As mentioned by Maberous the save files are larger than the maximum upload limit.
I have tried various dialogue options, including agreeing to serve him, and then changing my mind in a subsequent conversation.
In no combination, does Kolsc appear when I have killed everyone in the room.