Seems to me that Gettysburg was sort of an accident. Neither side chose to make a battle there, till the battle ensued.
Lee's forces were sattered mostly between Chambersburg and Harrisburg, so if Stuart was able to monitor the movements of the AoP, then I would guess that if the Federals were approaching, Lee would have sought to find an advantageous spot between those places from which to invite a battle. He wanted a decisive victory in the North.
If the Federals were not on the move, I suppose Lee might have continued to keep his troops in relatively nearness, but to invade major spots in Pa. such as Hburg and beyond, if not challenged. But in this case, I think he would have eventually been cut off and badly defeated, as you suggest.
I don't believe he would have done that tho, a road toward oblivion, so he probably would have sat tight at a spot to his liking and waited for the Federals to approach.
Wherever he was he did have that supply line problem and a limited amount of ammunition!
So, On with the speculation!