I have never used Evri to post an item, but understand they're not the easiest of Companies to receive information how to proceed with matters.
If you are happy to sell the item to this buyer again, personally I don't think I would, if they have already missed 3 delivery attempts, then you do have to wait for the item to be returned before relisting on eBay again.
When a delivery attempt fails for Royal Mail I know they keep an item 18 days before sending back to the sender, you could ask Evri if they do something similar.
@button.pants