If you always use your Iberia Plus card for flights or with any of the programme partners, your Avios will never expire.
In accordance with the Avios expiry rules, your Iberia Plus account must show at least one transaction (Avios collected or used) in the past 36 months to avoid losing the Avios you have collected. Transferring Avios (either issuing or receiving) is not considered a transaction. The system will automatically alert you at least 2 months in advance about the number of Avios that are going to expire. You will also be able to see this in your account statement, which you can check on iberia.com.
Once your Avios have expired, you cannot get them back.