You can actually see it happen in the video below from Dani Garcia. At the 1:00 mark, the player is killed while participating in an event. After respawning, the player looks through their inventory and weapon wheel to discover that their gatling plasma gun has gone missing. Then, at 2:25 in the video, the player catches up with friendly NPC Marion Copeland, who is now using the very same gatling plasma gun, which she apparently harvested off the player’s body.
Content retrieved from: https://www.pcgamer.com/fallout-76s-new-npcs-are-stealing-weapons-from-dead-players/.