My dad received a purple heart in Vietnam. Decades later somebody sole it. They stole other stuff to, but he mentioned this one quite a bit and not understanding why anyone would take it.
Somehow, he got a replacement. I don't know how or where it came from, but at some point after his purple heart was stole, I saw another one in his house years later.
If you lose medalls for whatever reason you can apply to receive new ones, although you've normally got to pay for the replacement. I'd assume the US military is similar in that regard.