If the tracking on the package says it was 'accepted' and 'departed', that means that SOMETHING was put in the SSK. USPS is not perfect with delivery confirmation or tracking and NEVER has been. Back in the day they would tell you specifically that delivery confirmation was exactly that...delivery confirmation and NOT tracking like everyone seems to think it is. If he specifically got 'tracking', then still, it says it was 'accepted' and 'departed' - something went was put in the SSK.
He's probably ignoring you because there's most likely NOTHING he can do and is choosing not to entertain all your ideas of him trying to rip you off. What could he possibly do? The package has left his hands and now he's probably just sitting there either happy he got insurance or praying the shoes turn up somehow.
Seriously, as a seller, impatient people are the WORST kinds of buyers. He did his part, you did your part, and it's no longer on ANYONE but the USPS, and the USPS sucks for a reason. They lose packages ALL THE TIME. I've bought shoes via USPS priority that have shown up, literally, 6 months later.
You submitted your claim and that's all well and good...but I would have given it a few days if I were you. Give them guy some credit...you obviously trusted him enough to send him a lot of cash for something sight unseen. Just because the USPS sucks doesn't mean every seller out there is a scammer, it just means that the USPS is not the most reliable shipping service.
If you're buying $1000 shoes you might want to go the FedEx or UPS route next time.