Keep logging out and logging back in, pray it puts you in a server where he's still alive. That or you can sit there and pray he respawns sooner or alter.
It sucks but hey, that's Fallout 76 (rant inc) same s*** happened to me btw, made me question tenfold why the hell he wasn't just included in a singular, player-only instance like what exists in ESO, or just about any god damn MMO. Even Borderlands had individual instances for players. I also don't understand why ghouls and dogs will consistently respawn in the overworld every 2 or 3 minutes yet an important quest enemy like this one will either take 30 minutes to respawn or not respawn at all. It's one of the many obnoxious things about this game.
~Gujin
http://i.imgur.com/39lX5ve.jpg http://i.imgur.com/9S9glYE.png https://imgur.com/a/Qxo9jXF