It wasn't as if the undead creatures had never taken over the ark continent. There had been cases of undead creatures taking over the ark continent. The undead creatures were stronger than their Masters. Although they were restricted by some laws, they could still break the laws and take over the ark continent if they were much stronger.
When Zhao Hai and the others saw the undead creatures worshiping the two undead creatures, they immediately thought of the undead creatures turning the tables on them.
