The outcome of the dispute or request the buyer has opened will largely depend on where they opened it (via eBay or via PayPal), and what (if any) kind of proof of postage you have (noting that the buyer's country can also affect the outcome of a PayPal case, as the buyer's country takes precendence when it comes to who is eligible for what under PayPal protections, for example in Australia proof of postage is required, but in the US, proof of delivery is required, so if a US buyer opens a PayPal dispute with an Aussie seller, proof of delivery is required).
If there was no tracking number, try putting the customs number (if you kept a record) in a universal tracking site, there's a few sites that will pop up in google search - the customs number isn't officially a tracking number, but sometimes they are scanned and tracked when they reach the destination country. You can also provide it to Australia Post to help identify and/or locate the package if you report it as missing, as internal records usually have more info than anything you can look up online.
Chances are, if you're not able to supply any proof of postage or delivery, the buyer will be refunded. Unfortunately I don't know how leaving out "The Kingdom of..." will affect whether you will have any recourse with the postal systems involved, but I would assume so purely because it's an explicit instruction (It's a shame no one at the PO pointed this out when you posted the package, though, I know they can't be expected to know everything, but that seems like a really important thing to know and advise).
