Its obvious he left. Does that really need to be shown?
I agreed. I was talking with my film lecturer about this scene and my argument was the same, after the scene with Rachel below, it doesn't make sense to actually cut to a scene to show the Joker running away just for the sake of doing so. That's unnecessary exposition.
Nolan gives the audience a lot of credit, you guys do not need a redundant scene to tell you the obvious.
Also I was watching the DVD again last night you can actually see Joker running out of the frame when Batman was diving out the window. He immediately left the scene of crime after pushing Rachel out the window.
I have been a fan of Nolan's since Memento and he is a director that will not leave anything unexplained. There will always been an explanation for everything in his movies. We just got to look for it.
An example being Gordan saying Dent killed five people. And for months it bugged me cause I only counted three (Wurtz, Maroni, his driver). Only recently I discovered during the scene when Maroni was entering his limo, at the far left of the frame you see one of his goon being grabbed (and presumably killed by Dent) while Maroni and another guy was entering from the right and for a long time I though that was the driver and then I rememeber, in the states, the driving position is on the left so make's in three person not including Dent in the car instead two.
Another cool scene is when they brought the "dead" Joker to Gambal. While Gambal back was facing Joker they were two of his henchmen next to Joker and it has also always bugged me how come they didn't do anything when Joker suddenly "wakes" up. Turns out, Joker stabbed they both as he was getting up.
Nolan's the man I tell you. He is never a sloppy director. Every single one of his scenes are meticulously planned and executed.