Hello.

If winner rejected win you should ask support for re-roll. If re-rolled winner used key, and it can't b activated by new winner - re-roll can be reverted and marked as received.

Winners are allowed to mark giveaway as not received, if they asked for re-roll and creator did not take any action. They can't use the key, so that key can be used by other user after re-roll is finally approved. Or used to create new giveaway if re-roll request was issued months ago, and chance is high that all entrants of giveaway already own game.