What if...? Response

If the Battle of Gettysburg had a different ending and the Confederacy proved to be victorious instead, it would definitely be a major loss for the Union. However, I don't think it would end the whole war immediately. Up to this point, the Confederates had won many battles. This battle would just be another one added to the rest. It might've weakened the Union's army and also lowered their morale too, but at this point the Union's motivation and confidence in winning was already dying out. So, the battle at Gettysburg would just be another normal win for the Confederacy and a devastating loss for the Union. However, if the Union had a really low morale and no interest in fighting anymore, Lincoln might have negotiated for peace with the Confederates. If they could see no chances of winning, they might have just wanted to stop the war altogether. But, we also learned that around this time, the Battle of Vicksburg also proved to be a significant turning point for the Union. This might've boosted their motivation to keep on fighting. Although the Battle of Gettysburg might've been a major blow to the Union, I don't think it would affect the outcome of the war.
Even if the South won, Britain and France still would not have given their support. These foreign nations already abolished slavery. Since the war now dealt with the issue of slavery and slavery had become a key factor, Britain and France felt that they should not go against their own policies and fight for South. They also felt that since they could get cotton from their own colonies, they didn't need to maintain trade with the South.
All in all, if the Confederates won the Battle of Gettysburg, it wouldn't affect the outcome of the entire war, yet it would still harm the Union.