I seem to recall one of the offers floated to Virginia by the rebels was that the capital would be relocated there should she join the Confederacy, of course leading to General Lee's famous "a capital for a nation is no profitable trade". So in short, Richmond would've burned instead of Montgomery!
But more in depth--I concur with everyone else in this thread that the war would not have ended nearly as soon. With the industry (however meager), troops, talented officers, and even pure land area of Virginia, the Confederacy would have been a much more formidable foe than IOTL. I imagine the Western Theater might have been much less active, as US and rebel troops struggled instead over Virginian territory. For example, New Orleans, might not have been so fiercely contested by the Confederates, and could have survived intact (that might just be my dreaming--I've always wished to see the old French Quarter).
It is even possible the US might have relocated its own capital, with Washington so near to what, in this TL, would be rebel territory. Perhaps Philadelphia, or even Boston? Going a leg further, it is even possible, though I don't think particularly likely, that the rebel troops might have succeeded in taking Washington at some point during the war. Whether this would have brought the North to the peace table, I doubt. But it is a possibility, however distinct.