In Nangong Yuehua's view, since the Sum Emperor had the power to easily detain them but did not directly attack them, it proved that he indeed wanted two people who could help him control the Ziyang World.
The fact that the Sum Emperor did not directly attack them was his greatest sincerity.
Since the Sum Emperor had already shown his greatest sincerity, and they did not want to leave the Ziyang World either, cooperating with him was not a bad idea.
The Cultivation World respected the strong, and even if they surrendered, it was not considered a loss; they were merely abiding by the rule that the strong are revered. Moreover, the Sum Emperor's background was extraordinary, and following him could also create an opportunity for them.
Not to mention whether they still had the chance to escape the Ziyang World, even if there was a chance, they might not have such an opportunity in other worlds.