I am guessing that Moriarty has left a scheme and video recordings behind rather than reappearing back from the dead. Although that would be a shame as I liked his interaction with Sherlock and something feels sterile about Sherlock fighting a scheme whose mastermind is already gone.

Still loved the sudden twist. I just wish they play Staying Alive over the credits or simply had everyone looking at the TV with the music playing allowing you to put it together anyway.