If Lee could not pull off a victory, it was over for State’s Rights vs. the Federals. The Union had broken on day 1. If not for Chamberlain, they would have broken on day 2. He truly believed that they would route at the sight of a charge as the weakened, tired units were moved there. Some units did, in fact, begin to retreat as the Confederates approached. Had the flanks been attacked as well, it would have been a closer thing. The Union used interior lines to move in fresh troops.
He did not believe he could pull back and deploy between the Union Army and D.C. or the morale of his own would fail. Lee tried an act of desperation and the gamble failed. In many ways, he fell into the same political trap that many on the North did, but he did not have the replacements for the troops sacrificed that day.
I strongly disagree that a living Jackson would have pulled off some miracle. Quite the contrary, the Jackson legend forgets that he made a critical, potentially war-ending mistake at Seven Pines, and that he could have done nothing more than Longstreet did (poor ol' Pete still gets blamed for Lee's foolishness).
To me the sign of a great commander is that he loses a smaller % of his forces than his enemy most of the time. In the Pacific in WW II, despite facing incredibly tough islands such as Iwo Jima, Okinawa, and others, Adm. Nimitz had the lowest ratio of casualties to total men employed in the entire war eclipsing the vaunted MacArthur. Well, Lee consistently had a higher % of casualties than his Union foes except at Fredericksburg---hard to lose that one!---and often lost the same total number of men as did Federal armies of about the same size. At Gettysburg, he lost a full 30% of all men committed to the action, an astonishing loss for a supposedly brilliant general. The supposedly inferior Union generals through the first 12 major battles or campaigns had a lower ratio of men lost to men committed than any southern general except at the aforementioned Fredericksburg, and leaving aside the obvious surrender at Vicksburg (a 100% loss to the Confeds that skews the data).
If Longstreet had rallied his troops to the Roundtops as ordered by Lee ,,, Chamberlain would not have affected the outcome of the second day .
The fact still remains ,,,,,, attacking the center of the fortified Union line behind the stone wall on the Tawneytown Pike was shear suicide and Longstreet and Pickett knew it before the assault began .
Had Stonewall been at Gettysburg history would have been entirely different . Stonewall made a living out of kicking butt when he was out numbered and in many cases he did it by attacking the end of their line or by flanking their line .
After all is said and done ,,, Lee did have to retreat as a result of his action on the 3rd day . Lincoln was really jerked at Meade for allowing Lee's Army to return to Virginia after the battle .
In summary ,,,, I believe Lee was P!$$ED at Longstreet and decided to punish his Corp.for not getting the job done on the 2nd day .