Steven Moffat has hinted that Moriarty is not going to return in the third series of Sherlock.
"Moriarty’s a one-shot deal in the original [books]. I don’t want [Sherlock] to turn into a show that’s about one villain and one hero,” said Moffat.
He also said that the show may continue to refer to the original books, saying;“Moriarty was great because he was a surprise. Every time you bring him back he won’t be as big a surprise.
“There are other great villains in [the Conan Doyle books] that we want to visit. We have to keep the show growing otherwise it won’t surprise you. Once you get the measure of it you’ll just get critical - if we keep surprising you and keeping you off balance you won’t.”