The gift recipient must accept the gift within 14 days to receive the item, but if they decline or fail to accept the item in time, it is simply returned to its original purchaser. Note that the purchaser in this case is unable to make use of any returned gifts themselves, but can resend it to the original or a different recipient.
You can view and manage your gifts from the “Gift Inventory" section of the Crown Store. From the Gift Inventory section, you can view your received, sent (claimed and unclaimed), and returned gifts, and it stores 14 days of gift history.