My preferred scenerio would be, Lee fights the first day at Gettysburg, Then orders his troops to withdraw to the Cashtown Gap, burning the town of Gettysburg as he leaves. The next morning headlines would read "Union Army defeated, Lee burns Gettysburg".

Lee then assumes a defensive position at Cashtown Gap having the high ground. The Union Army would be forced, because of politics, to attack Lee from a weaker position. A reverse Cemetary Ridge situation. After inflicting as many union casualities as possible Lee maintains his line of retreat back into Virginia.