You cannot return your miles without a loss. KrisFlyer miles expire after 3 years since they were earned and just 1 year if they were earned during promotion. You can extend miles availability but for that you will have to pay a fee and your miles won’t expire for up to next 5 months after. If you do not want carefully earned rewards to expire consider general travel rewards card like Discover it® Miles credit card. The card allows earning 1.5 miles on all purchases. All the miles earned during the first year will be matched at the end of the first year (if you are a new cardmember). For example, if you earn 35,000 miles, you will get 70,000 miles. Moreover, the card has no annual fee and all the miles you’ve earned will never expire.