How did Moriarity faked his death

For two years, those who were Sherlock-ed spent their most valuable time and filled up most of the memory space of their non existent and yet most desired mind palaces with theories of how Sherlock survived the fall. The makers of the show have done the most brutal things by not revealing how it was done but further depicting that something even more difficult and closer to the impossible happened at that same roof top . 

Jim Moriarty, the consulting criminal who shot his head off in front of Sherlock, returns. He is alive, going by the fact that nothing could be more awesome than him being alive. 

We thought for more than two years that Sherlock have beaten Moriarty, Hell he even beat death. But only to know that beating death is easier than beating Moriarty. We were forced to believe that neither of these two beautiful characters could bear an unfinished melody and hence were ready to kill themselves just to solve their final problem, but they were as they always have been, one step ahead of the audiences. 

Both of them must have figured out all the possible out comes that could transpire on the roof top of the hospital and had plans covering each aspect. But both of them underestimated (intentionally or unintentionally) each other and ignored the probability of the other one guessing their plan and arranging a defense for it. What I mean to say is that when Moriarty shot himself in the head, he must have thought that he leaves Sherlock with no choice but to commit suicide . But he didn't anticipated that Sherlock might also have imagined this scenario and must have had some counter for this too. The same thing goes with Sherlock, he also didn't anticipated that Moriarty can also fake his death and come back later on to finish the game. In any case, one has to admit that Moriarty's fake of death is better than Sherlock's. 

So now let me discus my theory of  " how he survived ?" 

Just to remind you all that throughout the episode, the Reinchenbach fall, people who shaked Sherlock's hands got shot . 

Remember those assassins who had to keep Sherlock alive so that they can get the computer code from him? Whenever any one of them saved Sherlock and shaked his hands they were shot. The same thing happened to Moriarty, In the last scenes he shakes Sherlock's hands and he is shot (by himself apparently). But this is what got me thinking, that all those assassins were instructed by Moriarty and obviously one of the instruction by Jim was to shoot anyone who comes near Sherlock (shakes his hands). So the important thing to note is that who ever shaked Sherlock' hands, was shot by someone else. What if we apply the same thing to Moriarty, what if his shaking hand with Sherlock was a signal for someone in the back building (or one of many snipers in the surrounding buildings) to shoot Moriarty in the back of his head with a fake bullet with a capsule containing blood. So what I am saying is that Moriarty's gun was empty it only made a sound and some one else shoot in the back of his head with a blood capsule and he fell down. We never knew whether there was any exit wound in the back of Moriarty's head. We just saw blood under it. On the other hand Sherlock didn't had the time to check as his friends were to die if he didn't jump at the earliest . 

Summing it up, Moriarty shaking hands with Sherlock and putting a gun in his mouth was a signal for his own sniper to shoot him with a fake bullet with a blood capsule in it, Moriarty's gun was empty and it only made the sound. He lied down with blood under his head but not any gun wound as there wasn't a real bullet. Hence he survived .