Confederacy's chance will increase, but Union will still have more chance.

Even though the Confederacy won, Union will still have higher chance of winning the Civil War. Confederacy wouldn't gain support from Britain or France, because for foreign countries, long war is better for them. If the war last long, that means there will be more trading during the war and foreign countries get more help. The war will also weaken the Americans, which means that there wouldn't be any attacks from America to other country or it will be easier for other countries to attack America. Even though they don't have foreign help, chance of South's victory will increase because it was first time that they won a war from North. That will greatly discourage North, and it will greatly encourage South. The reason that Gettysburg was turning point was because the North won two major battles in similar time, and if one of them turn out to be a lose, then it wouldn't encourage North as much as they did. Vicksburg, however, was a success part of Anaconda Plan, which was to divide the South into east and west. The loose of Vicksburg will also cause the South to have harder time trading or transporting their resources, since they used Mississippi River for transportation and trading. The war will last longer, and South has less people, less transportation, and less resources, which will cause South to have less chance of winning than North.