After Jonesborough the army fought at Lovejoy Station south of Atlanta and then headed north. From late September until November the regiment fought skirmishes at Dalton, Resaca, Mill Creek, Decatur, Florence, and finally reached Spring Hill and Columbia Tennessee where they fought until November 29th.
They then fought at Franklin (Nov. 30th) and Nashville (Dec. 15-16). After Nashville the army retreated to Mississippi fighting a rear guard action most of the way. So it is tough to tie down a date "before Nov. 29th 1864" near Atlanta.
The other possibility is that he was wounded in one of the battles between May and September and died later at a hospital. Most of the men wounded at Resaca, New Hope Church, Peachtree Creek, and Atlanta were sent to Atlanta and Marietta hospitals or they were sent to hospitals down the line from Atlanta at Barnesville or Macon or LaGrange. After Ezra Church (July 28th) the hospitals down the lines were the only options since the Marietta hospitals were in enemy hands. In other words, after Ezra Church most wounded men were sent away from Atlanta hospitals unless they were already there. It is unlikely that he would have remained in Atlanta after September 1st when the city was surrendered.
My suggestion is to order his records from the message board. I would also look up information on other McNeill's, McNeil's, MacNiell's. I noticed a George McNiel in the 37th Miss. Sometimes relatives have records mixed.