We have about 20 coins traveling the world. When one goes missing because the cache disappeared or it's been months since we heard of the cacher who retrieve or it's not in the inventory of the cache since a long time then, we make a duplicate using the same tracking number and start this duplicate on its new journey.
We do the same thing when a TB goes missing. We replace it by an other one.
For the moment, I only have one duplicate traveling. I have to go through all the others to see if someone has been missing for a long time. I'm a little behind because I spend too much time on the forum
I don't like it either when I don't find the real thing but, I do understand that some people are afraid to send a nice coin into the wild.