It will be difficult to prove the insured value.
Give the dealer more time; he is probably busy trying to locate it.
At the moment, there is probably nothing more for him to email than "yes, it is still lost" which you already know. So, just sit back and give it more time.
In the end, either the watch will be delivered in a couple of days or a few weeks, or it will be obvious it is never to be found and the dealer will reship.
Shipping problems is part of the business for our dealers. Sit back, trust them, and enjoy the watch when it or its replacement comes.
Good luck!