No, FlashBack licenses are not a subscription that you need to renew. They are a one-off purchase that is then yours to use forever.
However, each license is associated with a specific version of FlashBack. If a major new version is released, your existing license will not carry over to the new version. If you want to upgrade to the new version, you do get a discount on the license cost. Or you can simply continue using your existing version.
