It seemed the Master was gone at the end of “The End of Time”, but we all know he cheats certain death with enormous ease, and sometimes not even anything in the way of an explanation. But reportedly, not only has he been cast, but some of the old cast knows who he is. Sylvester McCoy let slip at a convention that he knows who the next Master is (though he wouldn’t say who) and that he will be “very, very scary”.
Sounds intriguing, for sure. ;-)