Did "two" McGahey's die under the same circumstances near Bolton?
This appears to be another one of the errors that can be found in the Mississippi Confederate Grave Registry.
From looking at census, marriage, cemetery, and the data found at this site http://www.rootsweb.com/~alcwroot/letters_mcgahey.htm
Thomas J. McGahey survived and lived in Lowndes County after the war.
He and his second(?) wife, Frances Ruth are buried in the Friendship Cemetery in Columbus.