The NPC is somewhere near it's original spot. In fact, you can /target it, and when you do /attack, your char runs toward a wall. It might be stuck inside that wall.
They're not in the wall. They are on a ridge above where they should be. Walk back, look up and you'll see them.
They just need to adjust the "z" of their spawn coordinates. Very hard right? Would take me 10 seconds.