Ledger's Last Performance?

Aside from just having finished The Dark Knight, Heath Ledger was in the midst of shooting Terry Gilliam's new movie. Now AICN has a report of a rumor about what will happen in the movie with Ledger's character:

The rumor is that at certain points during the film the main character, which was played by Ledger, fell through magic mirrors and, I would assume, into different realities or fantasy lands. The word is that each time this happens (3 or 4 times in the movie) the character will be played by a different actor and Depp would be one of those actors (which makes sense why he can fit this into his schedule), the other two being actors just as well known as Depp.

Depending on how this is handled, it could be a cheat, or it could be a great way to handle the situation with having the film half-completed. Maybe The Dark Knight won't be Ledger's last performance after all.