No, Really! How did he die?

Molly is involved, that I am sure of because of this:

Sherlock: “Molly, I think I’m going to die.”
Molly: “What do you need?”
Sherlock: “If I wasn’t everything that you think I am, everything that I think I am, would you still want to help me?”
Molly: “What do you need?”
Sherlock: “You.”

And then Sherlock told Watson to "Stop there!" As if he is directing Watson where he should be standing. Something's going on on the ground and Watson must not see it.

Then Watson tried to move again so Sherlock shouted "Stay exactly where you are!"

 

 Then Sherlock falls, now that's a mystery there, was Molly on the rooftop and managed to switch Sherlock with an already dead person or did Sherlock really jump? By the way, did you notice the truck right where Sherlock fell? Because right after the fall...

as John was about to run to Sherlock he gets knocked down by a bike. That's no accident it's all part of the plan, they need to distract John for a few seconds to execute the switch. Remember the truck? That must be where the other Sherlock is...

Or Watson could even be drugged, remember Baskerville? Maybe what he saw was just fed to him it did not happen at all.

 I'm not going anywhere, am I? Oooh, I think I'm going insane!