Since you already have a communication link with the opposing attorney, contact him/her and give them the insurance information. At the same time, be sure to advise them of the status (or lack of) the corporation and that there are no remaining assets.
In re-reading this thread, the attorney seems to have over-reacted (should have sent you a letter first), but I understand what he/she was doing. He was trying to get the corporation (or what remains) to respond to his claim. His r client's claim is against the corporation, in whatever form it currently exists, and not with the insurance company (the insurance company really insured the corporation, not the employees). By providing the correct insurance information to the attorney, he will probably still keep the lawsuit alive, but will attempt to resolve his claim with them. If not successful, he may continue to go after the corporation, but it is virtually non-existant at this time, so should be immune from further liability.
And you also need to contact the Corporations insurance agent. Advise them that the Corporation is being sued and that you expect them to investigate and handle the claim that occurred during the policy coverage period.