To tackle this problem, we have to consider the only two obvious answers. Jimmy is dead, and Jimmy is alive. If Jim Moriarty is dead then the problem gets shamelessly trivial. The GIF we see at at the end of His Last Vow could be a trick by another upcoming villain from the next season;or maybe it was Mycroft who put it there to scare everyone and force them to bring Sherlock back from his exile.After-all,Mycroft practically is the British Government. He can have access to every television in the country.He even remarks in the the episode that he doesn’t want Sherlock to go on the mission as he wouldn’t survive for more than 5-6 months.He cares for his little brother and would anything to keep him safe.It is even teased that there is a third Holmes sibling when a person from the Ministry asks Mycroft whether his denial to keep Sherlock in a common prison is an act of “brotherly compassion” Mycroft remarks “you know what happened to the other one”. In the books, Moriarty’s name is James and he has a brother too.So maybe, the guy saw as “Jim” Moriarty was just the brother.If this hypothesis is to be taken as accurate then the case is closed.
But Moriarty is too great a villain to die so easily. He is the ultimate nemesis of Sherlock. His equal in every sense.Maybe the show’s creators killed him off to early,realized their mistake and are trying to bring him back now.
Sherlock and Moriarty both are experts in crime. But Sherlock’s approach seems to be of a newly graduated med student, while Moriarty behaves like the Chief of Surgery. He has been there. His knowledge is more practical,more profound than Sherlock’s. Sherlock surprises with his analysis;while Moriarty charms.
In the first episode of S03, we come to know that Sherlock’s jump off the the rooftop was a part of his plan.He wanted Moriarty to think that he was defamed,vanquished;and finally pretend to suicide then dismantle Moriarty’s network all over the world in two years. But, THERE IS A GLARING FLAW IN THIS PLAN.How on Earth is Sherlock supposed to fake his jump by landing on the softbed if Moriarty is plainly watching everything from the roof?? Wouldn’t that ruin literally everything? Yes it would.So killing Moriarty was a part of Sherly’s plan too.The real beauty of that episode is not the miraculous jump.It is just as magic trick as Sherlock himself remarks.The real action happens on the rooftop.Every dialogue of the episode is a brilliant game of chess.Moriarty plans to discredit Sherlock and kill him, while Sherlock knows all of this, decides to play along and at the last moment,kill Moriarty.
Jim has planned to force Sherlock to suicide,which is something Sherlock senses comfortably before, and retaliates by crafting his own plan to murder Moriarty IN THE EXACT SAME WAY [suicide,duh!] Confused? it certainly is confusing. There are various theories regarding the modus operandi of Sherlock.That is something which will contribute towards another blog post.Now Moriarty is alive.It means he was aware of this scheme of Sherlock’s double crossing all the time, and in-fact triple crosses the Holmes bros. by faking his death. Thats why Mycroft calls his brother dear to tell him that “England needs you!”