You need to report it to eBay and read their very long description of what caan be done to get your money back - but basically I think it says that if the funds are still in the seller's Paypal account, they can fish them out for you, but if they aren't there's no protection.
I had this happen to me and ended up with nothing. It was only a small amount of money, so it didn't matter, but I would say eBay are to blame as much as anything. Your basic protection on eBay is that sellers don't want to lose their positive feedback, so a seller is unlikely to rip you off over a small amount of money. If however eBay terminates a seller's account while they have unsettled transactions, the seller no longer has any incentive to supply you, so why should they?