If you cancel your individual subscription you'll still be able to post results until the end of your current billing period. For example, if you were charged for your monthly subscription on May 5 but you cancelled on May 25, you'll still have access to the service until Jun 5.
Even after your subscription officially expires you can still log into your account via www.btwb.com to check past results. Just bypass the subscription page by clicking into your profile to view history. However, you won't be able to log any new results without an active subscription.
You can also export your results to a CSV file by logging into www.btwb.com, going to your Profile Page, choosing "Workout Posts", and clicking the "Export" button.