There doesn't appear to be a standard definition of recovery from chronic whiplash, also known as whiplash-associated disorder (WAD). Information on recovery after whiplash isn't even measured the same from patient to patient or from study to study. When health outcomes are measured with different tests, results can be varied and confusing.
Recently, a few studies on WAD have defined recovery for their particular research project. Recovery was defined as no pain or neck symptoms, minimum to very low scores on disability, tests, and successful return to work.
You may have to contact your representative or case manager at the insurance company to find out how they define recovery. Ask what basis they use for their definition. If you do not match their criteria, then you have a right to challenge the closure of your claim.