eBay won't get involved. It's up to you to pursue it with Evri - and good luck to you!
If your buyer uses eBay's money back guarantee to claim a refund eBay will check the tracking number - which I trust you uploaded when you dispatched it? (If you didn't,do so now!) If it records that the item was delivered, or even that delivery was attempted, yuo won't have to refund them. If it doesn't, you will.
