Aughra might just be missing the right words, seaphil-87-260699, because I think that she means that without something to stop them, the Skeksis will continue to have power outside of the stars which refers to their remaining untouched by nature. They would not be able to control the changes in the universe, but would stay immune to those. The Skeksis briefly claim perpetual reigning since they only need to perform the very easy tasks of murdering Jen and Kira to ensure their freedom. In a future of Gelfing extinction, the monsters, if any were still alive, would be unaffected by the next Great Conjunction. There would be nothing more to gain, and only a Gelfing can destroy the evil empire. Given that the alignment of the suns occurs once a millennium, it is unlikely that the Skeksis would witness the next one. They are not immortal, and if the emperor who dies is the original one, then it is due to the excessive rejuvenation that he has had access to. Eventually all of the Podlings' essence would be taken and the horrible creatures left to rely on biology alone.