See:  Wikipedia has a great article on The Final Problem - new member and cannot post a link. It explains the Reichenbach Falls in great detail. Sebastian Moran is Moriarty's chief protege and tried to take over what remained of his network following his (Moriarty's) death. Perhaps Andrew Scott will be brought back in that role but a different look.

I want to see them bring back Irene Adler - what a great character!