Shingi tied Nivlek tight enough that she couldn't move, and since she didn't seem to have high INT, since she was a Mage Type, he was confident that would stay in place. Still, he was ready. As for the hidden undead, they wouldn't act unless ordered, and only she could call them through the Black Crystal.
Still, he didn't plan to stay in this room, so after making sure that the knobs were tight enough, he told Wild Tycoon to pick her up, and they moved. The stairs were in the Hospital's basement, and its door was under the throne. But, of course, the location of the trapdoor leading down the basement wasn't the same as the Hospital was getting rebuilt each time the Boss got respawned and randomized a bit.
