No, I had solved the Duncan quest the non-evil way and already rescued Tania. I
returned now to the desert, killed Koan with a plasma disc, picked up the cube
and gave it to Duncan, earning the experience reward. Tania stayed friendly and
healed my wounds afterwards in Ewald's bar. There is a similar issue with the
miner: you can get his lamp for Iris, and threaten him to obtain his information.