Speaking at the London premier of Deep Breath Steven Moffat, when asked about a return for the Master, said that he thought the story for the character was finished once Russell T. Davies had told it.
The head writer then went on to say that the loss of Roger Delgado meant that the feel of the ‘great master villain who always loses’ was lost. Concluding by explaining that the Doctor doesn’t need a single arch enemy and jokingly apologising to John Simm.
Of course we know how much of a liar Moffat can be and an opportune moment to bring back the character may present itself in the future! The only way to find out is to tune in to BBC One on the 23rd of August!