John W Alexander and Sary Vestal of Putnam Co. Missouri

I would like to know what happened John Alexander the son of Moses Alexander and Sarah Bird. He was married to Sary Vestal abt 1878. They disappeared around 1900 according to John's mother's will after a family argument. I can't find him in the census after 1880. I am descended from John's brother and would like to solve our family mystery.