By the time Sherman became eminent the South was out of chances to win, the only question was just how many would die before the inevitable.
If Sherman hadn’t taken Atlanta when he did, Lincoln wouldn’t have been reelected and an end to the war would have been negotiated. Both sides were sick of it by that point.
The outcome wasn’t entirely clear in 1864. If Britain had recognized the CSA a lot of things would have changed. The point, however, was what Sherman knew, not the probability of the outcome. Subsequently Sherman employed his genocidal tendencies against the Plains Indians. He was a fascinating man, probably quite mad, and murderous.