Try this approach - purchase his death cert. from the state of Mich. On the cert. there is a box called "Informant". Sometimes it's a relative or a neighbor. It's a long shot. It worked once for me.
Here's the link to buy the death cert.http://www.mdch.state.mi.us/PHA/OSR/DEATHAPP.HTM
Do you know where she is burried. Try writing the funeral home that handled the services. Usually free.