I read about your search for your friend's ancestor from Mississippi. While the servant (slave?) may have made it back to Mississippi from Virginia, it probably took him quite some time to cover that distance. By then, say late 1863-early 1864, Harmon's Mississippi family probably wasn't able to physically get to Richmond to retrieve the body...the railroads were a disaster and there sure were a lot of Yankees in the way :)
I recall one of the largest hospitals in Richmond was Chimborazo and that most of their burials were in Oakwood Cemetery. Here's a link to the history of that cemetery:
Maybe someone has access to that cemetery's burial listings?
Did Harmon's service records mention which hospital he was in? Here's a link to the various hospitals in Richmond showning what records are available for each: