I wonder how far along Gilliam's movie is. If it's pretty late in filming, they might be able to get away with some "Brandon Lee-like" insertion in the film. If it's early, they could reshoot with another actor.
If it's in the middle, that's either a lot of wasted money or the movie itself is just as fucked as I thought it was.
Dark Knight isn't in jeopardy, but a reappearance of the Joker definately is. Not sure if they kill him off at the end of the movie (a la Keaton's Batman), or if they were planning on him appearing in the next movie. Harvey Dent (AKA Two-Face) is still in the works (with a damn good and intriguing choice of an actor), so no worries, though.
Rosalina: But you didn't.
Robert: But I DON'T.
Rosalina: You sure that's right?
Robert: I was going to HAVE told you they'd come?
Rosalina: No.
Robert: The subjunctive?
Rosalina: That's not the subjunctive.
Robert: I don't think the syntax has been invented yet.
Rosalina: It would have had to have had been.
Robert: Had to have...had...been? That can't be right.