Um, No?
I don't really have an answer for someone who comes to my office door and, seeing no one in the office next door at the moment, points into the empty office which I can't see into through the wall in between the two offices, and asks me, "He's not in?"

Um, if you don't see him, then yes, he's not in. Or no, he's not there.

You decide.

C.T.