My theory as to how Sherlock survived

Holy crap on cracker.

But that also means he would have been alive to see the exact look on John’s face when he thought his best friend died.

This is probably already out there, but oh well.

This isn’t a theory. It’s just something I want to point out. It deals more with Sherlock’s character than how he survived the fall.

When it comes to looking at the way he was falling, he was wildly flailing his limbs around. That shows fear – wanting to suddenly become a bird and flap your wings to keep yourself from hitting the ground. The body does whatever it can do avoid pain, so this is its reaction to falling. Someone who really wants to commit suicide would have already come to terms with their decision and would not be scared to hit the ground.
We already know that Sherlock had already figured out what Moriarty was doing, that’s how he arranged to have all this staged.
So imagine what must’ve been going through Sherlock’s mind when he was falling: “What if this doesn’t work and I land wrong and I die and all this goes wrong it can’t go wrong I can’t let this be my last impression on people this is not who I am what would happen to John oh poor John what a boring life he’d have without me” etc. His mind was racing with thoughts like those and how to maneuver his body to survive this fall. But his mind was so occupied that he could not focus on keeping his limbs from flailing around like that. That was his body’s reflection of his thoughts.

Now, none of that may have made sense. But here’s the conclusion:

Sherlock was scared. Someone who intends to die would not look like that as they fell to their death. 

I agree with the analysis in general but I do not necessarily agree that someone who wants to commit suicide cannot be scared. Falling, when you know how it will end, regardless of your objective, can be incredibly terrifying.