There is the issue of timing. After the hard fought assaults on Day 2, Lee was convinced that a similar attack the following day would succeed given proper support. So under a scenario of no Pickett's Charge, it would likely mean that Lee had become soured on the results of Day 2 in its aftermath and had decided not to offer further battle at the present location. That leaves 3 alternatives: 1) concentrate the army including Ewell's wing in a defensive position along Seminary Ridge and await attack by Meade; 2) withdraw the army through the mountain passes back to Virginia; and 3) heed Longstreet's earlier advice to turn the federal left flank between it and
Washington and await attack at a more defensible position. The most likely option in that case is probably no. 2; it would conserve the gains of Day 1 and put the ANV in a defensive position, which was advocated by Longstreet all along. Of course, that presupposes that Meade would be the attacker soon thereafter. If not, and Meade chose to wait it out, the ANV could not sustain itself for long without a reliable supply of ammunition, food, and forage.