When did this son John die? That is a point of reference to start with. Also I believe Ancestry.com which I don't have a subscription too has Ohio death records up to I believe 1958. You could make a specific request with subject line "Ancestry.com Ohio Death lookup date" then in the body of message give Rev. Merchant's Birthdate and last known place of residence.
Someone out there with a subscription to ancestry.com is bound to help you. I checked the Ohio Death Index online up to 1937 and did not find him. Unless he was still a young man and applied for Social Security in the 1930's then he would would have an application on file with social Security administration but I don't know when the Rev. was born so that is only a theory.