In the final scene on the roof with Sherlock, Moriarty schemes to have Sherlock jump from the roof. However, Moriarty has made arrangements to save Sherlock from dying. (I am getting back to the point about the suicide.) If Sherlock were to actually commit suicide, it would not only take away Moriarty’s only “distraction”, but also probably put a large target on Moriarty’s back as Sherlock’s brother Mycroft could very likely have Moriarty assassinated.
In the final scene, there is a person directly underneath Sherlock and Moriarty with some equipment on the bench. The equipment is an inflatable device (there are two large red inflatable bags with white markings and a gas canister in a green bag strapped across these. The person is on the phone looking up and down the street, waiting for a signal from or through Moriarty to inflate the device in order to catch Sherlock and prevent his death from the fall. This is Moriarty’s plan – to make Sherlock feel so beaten that he attempts to commit suicide, but then to prevent that suicide – thus “burning the heart out” of Sherlock, further solidifying Sherlock’s public disgrace (can’t even kill himself), and not running afoul of Mycroft (and his access to all manner of government resources).
The truck that pulls in after the busses is arranged for by Moriarty to hustle in the landing pad, and hide it from the general public. The people on the ground at the time are partly Moriarty’s people who would keep the public away so that the landing pad can be hidden away. So, the bike rider is actually Moriarty’s helper, not Sherlock’s as some have suggested.
The person under Sherlock and Moriarty may appear to be a person out for some shopping. However, the person does not get on the bus when it pulls in, does not have a purse, and the backs the person has put on the bench are heavier than plastic shopping bags and have large white markings (that is not reflection of the sun, which was behind clouds).
It seems like a rather clever and subtle plan from Moriarty, doesn’t it. But, Sherlock is one step ahead. If Moriarty wants Sherlock to think he is committing suicide, only to save Sherlock, Sherlock can foil that plan by actually making everyone think he has committed suicide. That would actually free Sherlock to infiltrate and destroy Moriarty’s network. As we know from previous stories, Moriarty doesn’t get his hands dirty and runs most of his network through email and texting. So, what would Sherlock need in order to impersonate Moriarty?… Moriarty’s cell phone. So, from Sherlock’s point of view, the last story also becomes Cinderella – if Sherlock can get Moriarty’s phone (like a glass slipper) he can impersonate Moriarty.