All you can do is open a not received case as soon as past the estimated delivery date.
If you do not do this and it ends up as lost then you lose, as no one will refund you.
Only if seller is using the equivalent of global shipping where delivery to the hub is all seller needs, and ebay is then landed with having make the refund.
If the seller is not using GSP, then they would have to refund, and then claim on the shipping company.