Assuming you used ebay's Simple Delivery you are protected if the item is lost/damaged in transit. That means ebay will pay the refund, not you, when the buyer opens a claim. So in future ask the buyer to open a "not received" case (or in the case of damage a return using "item damaged" as the reason). Then eBay will issue the refund themselves and you keep the original payment.
If you've already refunded there is nothing you can do now to get that money back.
