The history could be very different in the South had carried the day at Gettysburg. It would have to have been a very resounding military defeat, such that the Union Army would never be able to rise. But the South was deluding itself before the first shot was fired.
Modern historians are more critical of RE Lee generally and at Gettysburg specifically than previous generations were.
It's said that Lee wasted manpower the Confederacy could ill-afford when he would have been better off to fight a much more defensive war.
I think that's a big maybe, since Gettysburg was Lee's last big opportunity to make a war-winning stroke, and he couldn't do otherwise.
Indeed, had the Union army proved as feckless at Gettysburg as it had previously, there's no reason to think Lee couldn't defeat them decisively.
And I'm certain that's what Lee was counting on.
But Lee made mistakes, many of which we can easily recite, and the Union Army made far fewer.
So Lee's last opportunity for victory was gone, though it took almost two more years for the dumb*sses to figure that out.