Have you read your partnership agreement? Are there duties assigned to each partner? If so, let him play his “40% of nothing card” right into breach of contract

Have you read your partnership agreement? Are there duties assigned to each partner? If so, let him play his “40% of nothing card” right into breach of contract then sue for ownership of his shares and then hire someone to do what he refused to do. But probably, speak to a lawyer. You do need to respond to this offer in writing, even if rejecting it.