He had been at the post for two-and-half years, but it was never considered a great fit (he even acknowledged as much in his email to staff.) Besides, the studio had more misses than hits. "John Carter," of course, was the big disaster. No successor has been named. From the NYT:
Mr. Ross was a star television executive, running Disney Channel, when Robert A. Iger, Disney's chief executive, picked him to turn around the studio in October 2009. He had trouble from the beginning, hiring top lieutenants with little or no movie-making experience; together, Mr. Ross and his team faced the steepest of learning curves. Mr. Iger's hiring of Mr. Ross was heralded as a bold decision. Now his exit marks a rare blemish on Mr. Iger's record as chief executive, partly because of the selection of Mr. Ross but also because the studio continues to be in turmoil more than two years after Mr. Iger first moved to fix it. In recent weeks, according to Disney insiders who spoke on the condition of anonymity because they were not authorized to speak publicly, Mr. Iger began discussions with Mr. Ross about ending the experiment.