AS miles kind-of don’t expire if you read and believe the MP FAQ

https://www.alaskaair.com/content/mi...s/faq-benefits



However, the Terms and Conditions tell a somewhat different story:

“Account and mileage expirationMileage Plan miles do not have an expiration date and may remain in an active account indefinitely, provided that the Mileage Plan program has not been terminated pursuant to these conditions of membership. Activity in an account includes redeeming a Mileage Plan award or accruing mileage in the Alaska Airlines Mileage Plan program. However, notwithstanding any term to the contrary, if a Mileage Plan account is inactive for 2 years, Alaska Airlines may close the account, delete any mileage balance and reassign the Mileage Plan number. Deleted mileage can be reinstated for a fee for up to 1 year. To reinstate a Mileage Plan account please contact customer care.”

So according to that paragraph, redeeming miles is activity and restarts the clock. I don’t know if canceling an award and putting those miles will count as separate activity, but the (weird/confusing) way AS’s system works the transaction date of the redeposit is the same as the original redemption, so it wouldn’t give you later activity anyway.