I used to ship my wedding ring to my old jeweler in my old town, he’d check stones etc. The last time I sent it, it went missing somewhere between the large main city in our state and my local office. The local manager actually had the conveyor taken apart, found 4 other boxes, but not mine. The worst part was that they let me pay for the insurance, but then I had to prove the package met that value, luckily it went missing on the way from the jeweler so he could do the official appraisal.
I am sure it was internal theft as it was in my new state where the box went missing.
Some jerk stole it.
I would start searching online for similar works, maybe his estate can give you a valuation?