Frequent flier miles for air travelers who have not flown for some time can lapse after time-periods set by the airlines. For example, American Airlines’ AAdvantage and United’s MileagePlus miles lapse after 18 months of inactivity and Alaska Airlines’ Mileage Plan points expire after 24 months.
Many airlines offer renewal of expired miles on payment of a fixed fee. American Airlines charges $200-$600 depending on the expired miles, United charges $50-$400 while Alaska charges a fixed fee of $75 for up to one year of inactivity.
However, some airlines – such as JetBlue – do not offer reinstatement of expired frequent flier miles.
Read more details here:
Frequent Flier Miles Vanished? Here’s How to Get Them Back