On the first of January, almost the whole of the English-speaking world was glued on to their television sets or computers to catch the glimpse of a Sherlock one-shot special 'The Abominable Bride'. As the cunning writers Steven Moffat and Mark Gatiss have proven time and again that they cannot be trusted, we all were cautious about what the episode actually would be.
If you are someone who has not yet seen The Abominable Bride (oh dear) and does plans to watch it at some point in the future, be warned, this post contains spoilers and I won't proceed further if I were you.
For the lazy people, there is a TL;DR version below, scroll down to hell to read about it but a true Sherlock fan will never do that.
Let us first establish if Moriarity is really dead or no.
Fact 1: During the Abominable Bride, we meet the devil himself. Moriarty walks into Sherlock's mind palace (a lot of blogs refer to that as the dream, it is offensive). He enacts the same scene on top of the hospital as seen in the Reichenberg fall. If you observe carefully you will hear Moriarty speak the same sentence, basically, it is the reenactment of his death. But here he does something else, in the mind palace, Sherlock can see the back of the head that is blown off. So we can safely say, Moriarity did blow his head off, he was mad like that.
From this, we can deduce that Moriarty is absolutely dead and there is no doubt about it. There is no other point why Sherlock would imagine the turning of head in the mind-palace (And again this is not a dream. Also sidebar: Mind Palace is not something Sherlock invented, it has been practised for ages, you just didn't know about it.)
If we agree on this point, then the next question is- who broadcasted the 'Miss Me' message on the television screens across England? Surely, it is not Mycroft, who else has the resources to pull such a thing?
Before we begin to decude this let us take a stock of what happened towards the end of series 3 when Sherlock goes after the Napolean of blackmail - Charles Augustus Magnussen.
Fact 2: Magnussen was a media baron, he owned a newspaper and was notorious for blackmailing people. Sherlock had to trick his assistant, Janine hawkers, into an engagement to gain access to his private office.
Fact 3: Towards the end of His last vow, Sherlock shot Magnussen in the head against the orders of his brother, which was the cause of his exile.
From the two facts, we can deduce the following things - that Magnussen had a large network in the media and Janine had access to the same. You can't become the king of blackmail without having a media network.
Now we have established that, let's return to the episode in hand.
Fact 4: In the Abominable Bride, During the stakeout sitting in the shed, Watson and Sherlock discuss relationships and his physical needs. They also talk about Irene Adler, who, as we know, is hiding out in America. Remember, we are still inside his mind-palace and Sherlock is extremely high.
We can safely deduce that Sherlock is feeling lonely in his time. He is yearning for companionship. This fact is also highlighted when he observes the empty chair of Watson in his mind-palace.
Fact 5: During the conclusion of the Abominable Bride, Sherlock gives a big lecture of how we always forget the one person who is always there in the house. There is only one suspect- During that speech, his subconscious mind brings up Janine- his bride to be, that was abandoned.
When you eliminate all the possibilities, what remains, however improbable, is the truth. Thus, we come to the conclusion of the show when Sherlock says- a. Moriarty is definitely dead and b. His enemy has returned and is waiting for him at Bakers Street.
Final Hint: The title of the show was not the Invisible killer, it was not the mysterious death, it was Abominable Bride. Rather in another term, a diabolical bride, a cunning bride who has done some evil thing. There is one bride in the show who has risen from the grave to punish her husband and another to save Sherlock from the exile. Unlike the end of the Final Problem, Sherlock is not alone this time. There is someone waiting for him.
For the Lazy people out there- TL;DR
The episode successfully proves that Moriarity is dead and however loud the fan girls will scream, he is not coming back. Janine, however, is coming back and She with her media resources planted the 'Miss me' message to remind England of the value Sherlock brings to the country.
In conclusion, Sherlock and Janine will pick up where they left off.
P.s. As it is with these things, you can start hating me now.