That's unfortunate, but probably repairable once you find it again.

Had you played with the buddy box and a student before? It's a real blood-pressure event the first time you do, I know... cuz it was for me. And, it usually calms down after the first few buddy box flights, but you never know.

You didn't mention your method in your teaching process for approaches and landing, but I would hope that you did many many.. approaches at altitude, sort of false landings at, say 50 feet or so (as we say, two mistakes high) to get him used to making slow and deliberate approches that are on the runway centerline? If you did not, then perhaps that's how you ought to approach (no pun intended) his buddy box approaches and landings.. Then slowly decreasing his altitude until he is low enough to land.

You probably know all this, but sometimes a little reminder on how it may be better is always a good thing to do.

Best of luck finding the Nexstar and best of luck in your continued efforts to "bring another lamb into the fold"....

DS