In this scene we see Dylan waiting for the elevator, having just handed in his notice. He's travelling to the surface for the last time, effectively killing his innie self. We know this is the elevator to the surface as we've seen this painting before when exiting the severed elevator.

Nonsense. 1. The elevator is empty when it opens to Dylan, therefore, no need to switch anyone, therefore, no Ding. 3. How would it work ? Why would Milkshake let an innie go outside and do whatever the heck he wants ? It would be chaos. Besides, there's nothing telling he'd have that kind of power. Dylan innie is gone. We have to deal with it. (For now)