There is no "standard procedure" for informing an insurance company of a retirement. Usually this is done by letter. The fact that a claimant is resigning/retiring should have no impact on a current claim. The issue with every claim is whether or not the insured can work. If the medical records indicate that he can work, then generally his claim will be terminated.
Check out The Five Deadly Sins That Can Wreck Your Injury Claim for more information that could help your case.