Once you're some distance away from Sentinel Hill, Helix spills the beans, making a great big mess of your tank. After you clean it up, he finally explains, "The boss was in Sentinel Hill. She offed the last couple who flaked out, and I wasn't about to let myself be next."
How convenient that he waited this long to mention that. Do a 180 and blow up the boss. The ship still needs to go. Send Kearnen back to do the assassination. She might need help. Send the goblin back with her to tell her who to shoot. Everyone needs to stay on board for the ship. Assassination can wait.