As for where to bring that Human Emperor, Zhou Tian had already made a decision at the time.
Although Zhou Tian knew of some locations where the influence of the Main Plane's rules was not substantial, the actual influence of the Main Plane's rules in those places was only somewhat weakened. To truly affect the Undying Effect of the Human Emperor, the domains Zhou Tian had previously considered were essentially inadequate. Even if Zhou Tian were to take the Human Emperor to those locations, without the cooperation of his own Diligence, he simply would not be able to nullify the Human Emperor's Undying Effect.
So, after carefully considering the situation at the time, Zhou Tian knew his options were limited. According to the situation then, there really was only one suitable location for dealing with the Human Emperor, which was the world Zhou Tian had just recently explored internally.