Double Giveaway

Yes if he dont use it

No, in order for him to mark received he must activate the key. If he already has it then request a reroll

Short answer is No.
You could consider the key gone or if you are feeling generous and willing to trust in man's better nature, then you could consider 1) asking the winner to not share the key, 2) ask winner to unmark key as "Received", 3) ask the winner to agree to a re-roll, 4) create a support ticket asking for a re-roll, 5) present the same key to the re-rolled winner.