Why the coroner didn't realize they had the wrong body.

Molly is the coroner, and Sherlock had just gone to her for help; she has to have been in on it. I've been wondering if she provided a body to toss, but Moriarty was right there.

On the other hand, John saw Sherlock's face - so do we - and touched his hand while he lay on the pavement. Either that was a hell of a doppelganger, or what went over the side was not what was on the sidewalk within seconds.