"Woah, hey." Lost a student? Does he mean in the death sense, or the Door sense? Or, uh...both? 'Cause he's kinda come to understand that "both" is very definitely a plausible option.

"You...who?"

First Kate. And now - who the hell else, on top of everything? People who've been here forever, for longer than he has, who've felt like permanent fixtures to the city dissolving like they were never here.
Why even try?
But, hey. It could be anyone. Right?
This is why.