After I met Knurl I desided to let him go so I could fight him later after I visit Habitat and get better gear, the problem is that he is gone now and I only have an option to help him. I would accepted that if he would be gone for good or if I would need to find him somewhere else, but If I kill Harbinger he reappears on the same spot. Why I can't kill him after our talk later? That just limits player for no logical reason.