Militarily, even if the south had won Gettysburg, unless it had destroyed a large chunk of the Army of the Potomac in the process, what could it have done to capitalize on that victory? Taken Washington? Unlikely with the Army of the Potomac still intact and combined with the capital defenses. Not to mention that the Army of Northern Virginia would have had trouble staying supplied that long north of the Potomac river. Yes, Lee knew a protracted war would end poorly for his side. That's definitely why he took so many risks. His goal was always not to beat the Army of the Potomac, but to isolate large sections of it and destroy them. He was never quite able to accomplish that. It's a very difficult thing to do when you are outnumbered and outgunned. His best chance was at Glendale on June 30, 1862, but Jackson (who was overrated tactically but brilliant strategically) had a bad day.