Steven Moffat has said that the story is “sort of done” for the Master, ruling out a return of the arch-nemesis.
Responding at the London premiere Q&A, he replied: “No! I accidentally just said the truth! No, not really. I think the story’s sort of done. I thought what Russell [T. Davies] did with that was so brilliant, because I did think it was over.
“Once you’d lost Roger Delgado, who was so brilliant, it was tough to keep it… it’s like Moriarty in Sherlock – yes, I know – you think, ‘you’re a great master villain, you know what you do a lot, you lose! You’re always tremendously confident and then you’re humiliatingly defeated and you don’t remember that the next time you pop up with your ridiculous plan’.
“So no, the Doctor doesn’t really need an arch-enemy, so we’ll go for new ones. So, sorry John Simm.”