If it's beyond the latest estimated delivery date and the buyer opens a case under eBay's money back guarantee, you will have to refund them in full. If you resist, eBay will enforce the refund. You would then forfeit any return of fees and be penalised with an account defect.
Hopefully the buyer will repay the refund when their item arrives, but if they keep both eBay will do nothing to support you.
EBay is a very risky place to buy things.
