No Ball, No Clones, No Fish: This Is My (Fringe) Theory On How Sherlock Survived the Fall
I’ve posted a lot of non-fall-related Reichenbachian theories recently, but I suppose I can only put off addressing the big question for so long. How did Sherlock Holmes jump off a four-story building and live (plus what was up with him looking very dead on the street a few seconds later)?

Below is my theory on the matter. It’s a little different from other theories I’ve read so far, possibly because I’m coming at it with a different set of biases regarding what constitutes an acceptable solution to the puzzle. Or maybe because I just plain never liked the ball.
Beginning with the not-so-controversial stuff. Sherlock knew in advance was probably going to have to fake his own death, you know, unless a better option came up. He knew at least as early as when he ditched John to go see Molly and ask for a favor; that’s the first time he directly refers to it. This left him plenty of time in advance to prepare. When the time was right, he texted Jim and arranged their rooftop meeting so he was the one who picked the building. He played dumb about the key and about Jim’s plan because if he didn’t, Jim would have been suspicious of his choice. So far, so obvious.

When Sherlock asked for that moment of privacy on the roof and peered down over the ledge, he was checking out the progress of his homeless network, who had already begun to arrive and set things up on the street below. I’m aware there are no major curveballs in this theory so far. Bear with me.

During their last phone conversation, Sherlock not-so-subtly told John to stay behind the ambulance station, preventing him from actually seeing the point of impact with the ground. This should alert us to the fact that whatever he did to survive the fall was probably visible enough that he’d have needed to do something to block the sniper’s line of sight, too.

Since Sherlock couldn’t just tell the sniper where to stand, the obstruction had to be something he could bring in, ideally something that wouldn’t seem out-of-place for the setting. Now would be a great to time to bring up that garbage truck everybody’s so keen on, huh? Sherlock arranged for the sniper’s view of the pavement to be obstructed by the truck for the entire duration of the fall; it wouldn’t have lasted very long. Other members of the homeless network probably did what they could to obstruct of reduce foot traffic from the left and right of the landing point.
As for the landing: with John’s view blocked, the sniper’s view blocked, and the view of other people on the street limited, nobody worried a lot about being inconspicuous. Sherlock just jumped into a goddamed net.

Yes, I’m serious. If the homeless network is large enough to come up with a half dozen photographs of abandoned candy factories within minutes, I’m sure they could scare up a Browder Life Net given a few hours considering it was a standard piece of firefighting equipment until the (19)80s. And if we’re figuring Sherlock actually brought stuff to the scene, why wouldn’t he choose to leap into something specifically designed for leaping into? Something made with people jumping off four-story buildings in mind?
These things are portable, they set up in seconds, and presumably, one wouldn’t look like much lying on the sidewalk unfolded, particularly with a bunch of people standing around to obscure it. Also, since they fold, it would be the easiest thing in the world to cart Sherlock off the scene in one without anybody noticing a thing… especially if that garbage truck was the side-loading kind.

So: Sherlock fell into a life net, the folded net was tossed in the truck, and the truck drove away. That works, but it leaves us minus a body. Fortunately, while all this was going on (or slightly before or slightly after, depending on the how the timing shakes out) another body was dropped from a window by Molly and/or another accomplice who has access to the building via Molly. It’s this one, the one we actually see hit the ground:

This other body only bears a slight resemblance to Sherlock Holmes, much like the kidnapper who scared the little girl only bore a slight resemblance to Sherlock Holmes. It’s not the kidnapper though. It’s just some tall dead guy from the morgue who may have been given a dye-job and a very cool coat. Molly provided him, and helped with whatever was necessary to maximize the resemblance. Once he landed, the fake doctors of the homeless network may or may not have splashed some blood around to complete the effect, depending on how far it fell and how much dead guys bleed.
This is the only body we actually see at street level.
By now, if you haven’t given up on me entirely, you’re probably wondering how I’m going to explain the fact that he appears to look so very much like Benedict Cumberbatch when we finally get a shot of his face:

My answer is John Watson.
As John was running around the corner, he was completely convinced the person he was about to see on the pavement was Sherlock. He’d just spent several very intense minutes listening to Sherlock’s voice while watching him and being told to keep his eyes fixed on him. He was at that moment in a panic and 100% Sherlock-focused. And then he was clocked by a bike.

In fact, John lost sight of Sherlock twice — first because of the building and then because of being knocked over by the cyclist — but those seconds-long interruptions only intensified his focus on the object he was trying to keep in sight. In fact, he was quietly repeating “Sherlock” to himself as he picked himself up off the street and walked over to the body.

Ultimately, he sees the corpse’s face for only a few seconds. This is the condition he’s in when he sees it:

John saw Sherlock’s face because he already believed the body was Sherlock, and because he was in a compromised state. An exact clone was not necessary. The Baskerville drug was not necessary, although that episode does establish precedent for the camera seeing what a character sees instead of what is actually there.
It’s enough that he’s just in a heightened state of emotion and has recently slammed his head into the concrete. He had a concussion, and thus was a very unreliable narrator.
Such is my Reichenbach theory. I can’t say for sure this is the explanation of events Moffat, Gatiss and co. will choose to go with next season. They might choose to make it a lot more complicated, or a lot more about frame-by-frame viewing. But personally, this is the one that’s working for me, if only because it’d be a pretty good use of that whole “it takes less to fool people than you think” theme they spent a lot of time setting up in this very episode.