I definitely agree there was a body switch on the pavement. John was delayed getting there and his view was obscured, so there was definitely opportunity there. Some fake - or probably real but not his - blood and Sherlock playing dead and Bob's your uncle. The fact the medical staff moved him without putting a neck collar on and putting him on a back board is suspect too - like they knew it wasn't needed and their job was just to as quickly as possible get him away from John and anyone else who might spot he wasn't actually dead or hurt.

Not sure who or what took the fall though. :D I'm going to go check it on the iPlayer to see the exact sequence again and what John (and us) could and couldn't see through the sequence of events and where a switch could have occured on the roof. I keep thinking about that dummy that was hanging up in the flat earlier. Not that I'm saying the dummy was used, but that was about an apparent suicide that wasn't really one too, so it was setting us up for something.