So I have no idea is this is anywhere close to correct, but I’ve read and watched many theories about how Sherlock survived. I believe that with Molly’s help, he had a body made to look like him put in his place after he fell. But I can’t stop wondering who the body is. Maybe it’s just some random unimportant detail but I just feel like it’s not.
My theory is that the body is the same one that Sherlock abuses with a riding crop in the beginning of A Study in Pink. We never see the face of this body, but we know he worked there and Molly knew him. From Sherlock beating him with he riding crop, the body would be bruised. If Sherlock fell to his death he would surely have some bruising. Since the body would be kept in the mortuary of the hospital, it would be easy for Molly to get it out onto the street where Sherlock falls. I don’t remember if there’s a major time gap between A Study In Pink and The Reichenbach Fall, but the body could be kept fresh in the mortuary.
I think Molly made the body look like Sherlock and then swapped them. Maybe I’m completely wrong, but it makes sense to me.