HOUSTON — Irma Johnson never really thought of herself as a crusader. But the quiet widow from The Woodlands has been featured in a Michael Moore movie, watched her story retold on “Good Morning America” and is trying to let others know that their employers may have purchased secret insurance policies on their lives and stand to profit handsomely when they die. The industry darkly refers to the policies as “dead peasant” life insurance. And but for a post office error, Johnson might not have learned that when her husband, Dan Johnson, died of brain cancer in 2008, the bank...