Unless Moffat is playing games it will be simplest explanation due to Moriarty’s whole ‘sometimes things are simple’ spiel on the roof.
The “make believe” art message on the reporter’s wall.
The stress on “it’s all a trick, a magic trick” in the phone call to Watson.
Misdirection (of both Watson by biker and also TV audience) – we see a body hit the floor but not necessarily as a direct effect of the fall. My guess (as above) is a fall into a hospital laundry truck or similar organised by Molly then the Sherlock double from the kidnapping (presumably killed by Sherlock hence the whole “I might be on the side of the angels but that doesn’t mean I’m one of them” comment to Moriarty – be interested to see how they write Sherlock finding his double though) is thrown onto the pavement.
Great TV and still my favourite thing on the box visually (direction, cinematography) at the moment.
slainte 8) rob