Huh? There would have been nothing between Lee and Washington at that point. Maryland was very much sympathetic to the south... forced into the Union by jailing politicians without a trial. Grant would have been forced to return to the area... possibly putting Vicksburg back into play. Everything changes if Lee wins at Gettysburg.
Except what was left of the Army of the Potomac and the Washington D.C. garrison manning the dozens of forts protecting the city. Lee would have about 45 or 50 thousand men, little ammunition, and thousands of wounded. Too little for a siege.
Maryland was very much sympathetic to the south... forced into the Union by jailing politicians without a trial.
Maryland's sympathy that you speak of certainly wasn't on display the year before during Lee's campaign in the North. It was a divided state, to be sure, but your suggestion that it's sympathies lay overwhelmingly with the South are exaggerated.
Grant would have been forced to return to the area... possibly putting Vicksburg back into play.
By the time Grant is recalled, Vicksburg is already lost - it surrendered on July 4th.
Everything changes if Lee wins at Gettysburg.
Sorry, but in the long run nothing changes. The South still loses.