Oh dear, you sold a high value item and didn't send by tracked post 
As far as the payment being released is concerned they you will have to wait I'm afraid, perhaps up to 21 days.
If you mark the item as dispatched but don’t upload tracking information, funds should be available seven days after your latest estimated delivery date.
If you don’t provide tracking information or mark the item as dispatched, funds will be available in 21 days.
https://www.paypal.com/uk/webapps/mpp/security/ebay-payments-learn-more
Where no tracking is uploaded, eBay will check for feedback four days after the estimated delivery date - if it has been given they'll release the money.
In addition if your buyer claims non receipt then unless you can prove delivery then you would lose the case so would have to refund. You could make a claim to RM for a lost package but as you didn't use the most appropriate postage method they could refuse the claim.
Hopefully the item will arrive safely and you have an honest buyer.
