One of my favourite scenes in that film is when Marty arrives back to 1985 at the end of the movie. He races back to the mall just in time to see his earlier self jump in the DeLorean and vanish.
Or so I thought.
I realised some time ago that it's not 1985; it's 1985(i). A parallel world where the "Twin Pines Mall" is the "Lone Pine Mall". Where George(i) McFly is a successful writer, and smugly lords his success over auto-detailer Biff(i) (who, by the way, seems to be suffering some sort of severe emotional damage)