I was playing the last day and I put Piper in the school for some training, today I see a fire so I sent many dewllers, for my surprise Piper was gone, I cant find her grave. How can I get her again?

If on pc try "player.moveto 2f1f" to move the player to piper, in the console.

Dwellers can randomly disappear without reason, I've lost three regular dwellers so far. I don't know how to get them back.