We mailed a zillion things and only had 2 go missing - in the same week! But we shipped them all *insured*. Still that did not help at all in finding them, nor did the PO ever pay up.
Good thing they were not really expensive itmes.
Then we had a crazy mix up when ds moved out. Even though his name is not the same as his dad's, they sent our mail to ds and his mail to us. And ds moved several times, so all of our mail was all over the state - UGH!
I finally got so mad I sent an email to usps's website and reamed them a new one.
Took them a couple months to get that fixed.
If I were you, I would go to that website and report your loss. Not like they'll find or replace your guitar, but someone should hear about that. Good luck.