"the tailcone seems to be intact in the photo; these passengers are using airstairs, not an emergency exit, are they not? Please correct me if I'm wrong."
You're right - the tailcone is intact in this photo. However when it IS used as emergency exit the cone gets jettisoned. Opening the rear cabin door, when armed, will send it on its way. When it is not armed it can just be opened as in this photo.
If I remember correctly, DL's MD88's make the tailcone fall by gravity, while the MD90's have a some kind of "charge" that helps them on their way, although it's been a few years - my memory could be fading on that point.