I have to admit I wasn't aware that someone could be awarded IB for life!
However, as IB claimants are being migrated to ESA over the next few years then you will have to undergo a different assessment called the Work Capability Assessment unless you fall into one of the [very] few exemptions. If you look in the Members Section under the ESA guides and also the Members Only News items you'll find a wealth of information regarding the migration process.
Nothing on this board constitutes legal advice - always consult a professional about specific problems