If that happens, and it does, then it's between you and the buyer, to receive a refund.
Nothing can be enforced through eBay, you need to rely on the buyer's honesty to repay you now, they have received their item.
This can be done through a cheque, bank transfer or r a PayPal Friends and Family payment, or you can send a PayPal invoice.
As said, nothing can be enforced for the buyer to repay you.
@pinkprincess39