eBay will not automatically refund the buyer's money , but in future never let an item go without receiving that code, because the buyer if dishonest, could open a case for item not received, as you have no proof of collection they would receive a full refund.
There are also chargebacks a buyer can turn to , so for future collection items as said, just politely message the buyer that they need to bring that code with them on collection, as the item cannot be released without it.
@lynseyboo1