I believe the Minister said they were not insured in part because their value "was astronomical." So I was not quite correct. But, of course such premiums would be very high. Given what we see of security now, I would assume any insurance company would deem them "uninsurable" at this point. If insurance were provided, said insurer would dictate far more stringent security.
If these items are found to be replicas, then I guess the joke is on the thieves. But there would be catastrophic fallout for the Louvre as well.