How did he survive?

[John Watson]

Okay, so, we all know that Sherlock jumped off ot St. Barts in Reichenbach and Jim killed himself so, what are some speculations on how he did it? You know, besides the obvious one that the TARDIS caught him . Joking! And how did Jim survive the shot to the head?

[Molly Hooper]

Molly maybe helped him out there And Moriarty probably used a fake gun with a pack of blood handy. At least that's my theory.

[John Watson]

That was my speculation to. Then I saw the most obvious clue of all, eliminating that idea. HE IS STEVEN MOFFAT! KING OF TROLLING! HE HACKS INTO WEBSITES TO TAKE OUT THE SPOILER ALERTS! He couldn't do something that simple, at least I don't think he would.

[Sherlock Holmes]

I don't think that he is like Mycroft and able to do that. However, he could lie and say that no one has managed to get the correct idea.

I believe that we must look at the smaller details. For instance, the IOU in black wings by 221B Baker Street, which can be see when Sherlock is arrested and when John is catching the taxi to get to St Batholomew's. In Kitty Riley's house, there is writing on her wall: Make Believe.

Another thing to consider is why does Morirarty owe Sherlock a fall? The detective has done nothing to bring down the consulting criminal. Therefore we can deduce that something else could have happened between the two. Similar to how Watson was not present when Moriarty first visited Holmes in the book 'The Final Problem'. We also know that Holmes survived the fall and we only think he fell because Watson deduced that. He didn't see the actual fall. Could Sherlock's survival be based on this? There is a theory that the Baskerville drug was used on John.

The most common theory on Sherlock surviving is either he leaped onto the truck, then ontothe ground. The ruck being designed to break the fall.
Or there was someone looking like Sherlock (The scream) and it could have been that person falling. Or Moriarty used a mask, and Sherlock used that to out on the consulting Criminal's face before shoving him off the building. I believe we can rule this one (Or both out) out as it had to be believable for the gunmen,

We may need to also consider why Sherlock looked panicked when Moriarty killed himself. Was it for show, so that the gunmen would completely believe Sherlock's fall? Also, it wasn't part of the 'to-do list', if you will, for Sherlock to leave a note. So why do it? Why make sure that John sees him jump?

And on the subject of Moriarty, either he did kill himself as he loved the game too much, like Irene. Or he used a blank shot, a fake gun would probably be recognised by Sherlock. Either way, it has been revealled that Moriarty isn't going to have much of a role for the next series, so it is possible that the character actually did die. No offense meant to Moriarty.

EDIT: What if Molly was a red herring? What happens if he just needed her to help John get through this? Its Sherlock Holmes, the obvious is possibly red herrings, as we need to think.

[Rose Harrison]

I do think Molly helped Sherlock fake his death, but as for Moriarty blank shot is the more likely idea. Sure, it could have also been just to help John through, but I see this as unlikely, because Molly would be having just as much struggle as John, as we ought to consider she does care about Sherlock, apparently a lot.
And plus, John and Molly don't actually know each other as well as they both know Sherlock, so it would probably get awkward with one trying to comfort the other. It was heartbreaking though, the way John was saying 'Please, he's my friend, just let me through' I nearly cried, his face was so sad. But he was hit by a bike I think and something could have happened there, but I doubt it. And anyway, where was Molly when Sherlock fell, if he told her he was going to die she should have been there too.
But again, why make John watch him fall? I have a theory for that. However he did fake his death he wanted to make sure that at first John thought it was real, before coming back. Because then, John might go telling someone that Sherlock wasn't dead if he knew that Sherlock had faked his death. I think somehow Sherlock knew that Moriarty wasn't dead, which was probably why he looked worried/afraid when Moriarty shot himself. Then again, he could've been scared that he'd be bored without him alive which I'm seriously doubting right now.
Anyways, throwing Moriarty off the roof wouldn't work because that would kill him. Plus John was watching him, Sherlock wouldn't be able to put a mask or anything on Moriarty and then drop him without John being able to tell. So, yeah. I have no idea how the amazing Moffat did it, but one day if he doesn't tell us I'll simply hunt him down and make him tell us how Sherlock and Moriarty both survived, and if Molly helped Sherlock at all.