No reference to George Maupin in the History of Callaway County after 1862. Unfortunately the Fulton newspaper was shut down for having Southern sympathies right around the time of the massacre.
Findagrave: George Maupin, died November 1, 1862, buried Dry Fork Cemetery, Guthrie Township, Callaway County, Missouri. Guthrie Township is in west Callaway County. Depending upon how the districts were drawn, its possible Givens resided in Maupin's county district and Maupin was present on behalf of his constituent.
No further info on George yet, but his son Addison B. Maupin was reportedly a leader in the Callaway County Republican Party throughout the war, which qualifies as an indication of being a "staunch unionist." Addison moved to Bates County after the war. Looking for possible bios on Addison referring to his father dying of wounds received from Federal troops during the war.
Other children of George Maupin--William Taylor Maupin; Amanda M. Maupin; Nancy Richardson Maupin Jamison; Mary E. Maupin Moore