If you decide to cancel your paid membership, you will keep the books you unlocked. These are available for you at any time to listen to, even if you decide to cancel. However, any unlimited titles that were in your library are unavailable once you decide to cancel.
Please keep in mind that you can’t use the purchased coins after you cancel. These coins will be kept in your wallet for 5 years, and you can use them again if you decide to reactive your membership in the future.