The CsA can’t win a late war. By the mid-late 1863 it was just a matter of how long until the south stopped kicking.
I'd argue the Confederate Army was afforded many opportunities for 'decisive victories' even after the infamy of July 1863 and its popular/romantic connotations, all of which could have contributed towards the reality of a 'negotiated peace' in 1865. The North, after all, experienced its greatest crisis of the war in Summer 1864. For examples of lost Southern opportunities after the tripartite strategic reverses of Gettysburg/Vicksburg/Tullahoma:
Proper Attack at McLemore's Cove
Coordinated Assault at Chickamauga/Hood Avoids Wounding
Siege of Chattanooga Not Lifted
Lee Fully Outmaneuvers Meade, Bristoe Campaign
Longstreet Maintained at Missionary Ridge/Outmaneuvers Burnside at Campbell's Station
Meade Attacks/Lee Counterattacks, Mine Run
Taylor's Flanking Assault at Pleasant Hill, Banks/Porter Effectively Pursued (Red River Campaign)
Longstreet Not Wounded/Gordon Attacks Earlier, the Wilderness
Beauregard's Plan for Drewry's Bluff
Hood Attacks at Cassville
Lee Not Debilitated at North Anna
Lee's Offensive Plan at Cold Harbor
Johnston's Napoleonic Strategy for the Defense of Atlanta, Forrest Operates Against Sherman's Supply Line
Lee Reinforces Petersburg Before Grant Completes His Crossing of the James
Early (Briefly) Captures Washington
Johnston Directs Peachtree Creek, Capture of Atlanta Delayed