HeatVision reports that Robert Downey Jr. has left Disney's Oz: The Great & Powerful which is being directed by Sam Raimi (Evil Dead & Spider-Man Trilogies). The site expects Johnny Depp could very well step in to save the production for the studio. It would be a safer choice for Disney as they have a strong relationship with Depp and he's already been involved in a re-imagining of a classic story with Alice In Wonderland.
The only issue would be his availability since he's starting production on Tim Burton's Dark Shadows next. Depp will also be busy starring in three other Disney films with Lone Ranger playing Tonto along with Pirates 5 and Pirates 6. The last two have been rumored to be shooting back to back. The site mentions that Oz is further along than Ranger and could start production in the second half of the year.