From TV Guide:
Multiple sources are telling me that Isaiah Washington will not be returning to Grey's Anatomy next season. An ABC Studios spokesperson confirms that the actor's contract option has not been picked up, but declined further comment.
One insider, who requested anonymity due to the sensitivity of the situation, speculated that the decision was likely due only in part to the T.R. Knight homophobic slur scandal and the subsequent fallout. "There was a pattern of problematic behavior going back before he used the F-word," says my spy. "I imagine [his dismissal] was the result of all of that."
Washington's rep, Howard Bragman, confirmed the news, adding that his client was informed by Grey's executive producer Shonda Rhimes earlier today that he was not being invited back to the show. In a statement, Washington, referencing the iconic line from Network, said, "I'm mad as hell and I'm not going to take it anymore." (He's kidding... I think.)
Plot-wise, it won't be difficult to explain Washington's absence. In last month's season finale, Burke left Cristina at the altar and moved out of their apartment.