Whether it was stolen or fell off, it's gone now. I feel for the OP poster as well as it really wrankles me when people steal stuff.
Now back to the 'fell off scenario'. I've seen so many things fall off over the years and have dodged many things on the highway/freeway. It is so extremely dangerous when things fall off as you all know.
If it's possible that the bolts can come loose, that should be on the inspection list before departure.
Just the other day, I noticed a piece of metal in my driver's side tag tire. It did cross my mind that someone might have wedged it under my tire for me to roll over. I didn't pull it out as I made that mistake with my SUV once when a nail was in the side wall. I pulled it out and air started coming out so I put it back in and the air stopped escaping. I drove straight to the tire store.
While I was in for an oil/filter change on the coach, I had the tech look at the tag tire. The metal piece was just in the tread, no air loss (dodged $1000 bullet as Michelin 365's tires run about that at the Prevost shop).
Safe travel to all, keep everything glued down!
MM.