@Iberia_en tweeted out:
Hi, sorry for the late reply. Yes, the flight must be used in order to validate your promotion purchase: [promo URL] /1
If the customer requests a flight refund, either because it is permitted by the fare or for any other reason, the promotional Avios will be withdrawn from their account. This applies for no shows as well. Kind regards. /2
Not sure if that makes sense - what if I booked a flight yesterday for 1/1/2019 and am unable to fly it before the promotional Avios would be withdrawn?