Rider's words made sense. After all, Mercury Lamp was just a visitor from another world. With all transmigrators being sent back, her departure would happen within a month, tops.
Of course, there's always the remote possibility that her world might never be discovered. The Endless Void holds countless worlds in corners that we currently cannot detect, but the likelihood of that is minimal—such distant worlds almost never experience transmigrations with our universe.
Transmigration occurring implies proximity between two worlds, and two worlds drawing near each other could hardly escape our increasingly powerful spacetime detection.
