As you have tracking proving delivery, and presumably to the address provided by PayPal on the payment confirmation email, and have added the tracking number to the Ebay transaction, the case will automatically close in your favour. That's the whole point of tracking.
If you shipped to a different address, eg. one the buyer supplied after they'd paid, or you wrongly posted to the one on the Ebay order confirmation (which is the buyer's Ebay-registered address and not necessarily where the buyer wants it sent) and not to the one on the PP payment confirmation (which is the actual delivery address), you will have lost seller protection, and the case should close in the buyer's favour.
If you're sure you did everything correctly, then the buyer should check with family members, around the property, and with near neighbours. This almost always turns the package up.
But if not, the buyer will have to take this up with the carrier themselves. If the carrier misdelivered and can't retrieve the package (or they discover they have a dodgy delivery driver or postie on their hands), they, the carrier, will have to compensate the buyer.
If the carrier can absolutely prove that the package was delivered to the correct address, then the buyer's only remaining option is to report the package's theft from their property to the police.
@denise43cat
