he can prove it.
DPDs systems show it as being delivered.
thats proof enough in ebays eyes.
Ebay will want a signature...the seller cannot provide this so no, he can't prove anything.
"Proof of delivery” is online documentation from a postal company that includes all of the following:
A status of “delivered” (or equivalent in the country to which the item was delivered) and the date of delivery.
The recipient’s address, showing at least the city/county or postcode (or international equivalent).
Signature Confirmation for transactions that total £750 or more.
That's eBay's seller protection. If the buyer appeals this is an open and close case.