They are 'reborn' where they first started, only they become more and more a part of the environment as their minds break down more. Any progress they made towards the peak where the revival door/gateway is lost and only the first person to go through the door can be revived leaving everyone else in this place. Although it is vague as to whether it is from MC's original group or of all the people that were brought there over time. If it is the later then it means that no one has ever been revived.