I know I'm way late to the party, but I still gave it a good long think, considering all aspects of the problem before trying to envision a solution. What seems the best solution to me is to return along their own starline, use the several weeks of delay given to evacuate as many people as possible from the connecting colony Huygens (which from the intro is the colony the ship came from through the starline), and then destroy that system, cutting humanity off from the Super Happy Fun aliens, at least for now.