You never have to worry about losing your data when using CrossFit btwb.  All of your data is tied to your personal account which exists outside of your subscription, gym, or coaching program.  Data will never be lost due to a change in your subscription, or if you discontinue your subscription entirely.  If for some reason you cancel your subscription you will still be able to view your previously logged data, you just won't be able to add anything new to your account.