did Molly provide a body to "be" Sherlock?

That’s my guess. I’m also surmising that she is the one who did the autopsy.

Keeping an ant farm thriving, or a lapdog alive and well and happy is much more of a challenge

You're assuming that the methods chosen for destruction are straightforward. Which is not very Moriarty at all. I mean, he could have just shot Sherlock if he was really doing the analog of smashing an ant farm. However, tricking a lapdog into killing itself sounds more tricky and less monotonous than tossing food at it twice a day.

I tend to be in the camp that Sherlock jumped t insert handwavium to be explained in 3/1 and was on the sidewalk when John got there. However, if anyone is actually in the ground, then it's not Sherlock (I like the poetry of it being Jim). I think the key aspects that Molly managed were "doing the autopsy" and "identifying the body"

Didn't Watson make it to the body and see Sherlock's face? I guess plastic surgery on corpse is easier than on a live person cause you can use that filler stuff morticians use.

In terms of pets - a heck of a lot more to them than feeding them twice a day.

In terms of survival. People do survive falls from great heights. One secret - being relaxed which Sherlock could manage. A second: land on your feet, bend your knees and roll. Did we see how Sherlock landed? I seem to remember him landing flat. Third secret: land on something soft or at least springy. Sherlock landed on a concrete sidewalk. Maybe Sherlock had mat there that only looked like part of the sidewalk. So - did we see him land or did the camera pan away at impace. Because if we did not see him land he could have met all three criteria for survival of a fall from a great height.

He could have made himself up between death of M and his jump to look like corpse. And as others have said Molly could have taken care of autopsy and finding Sherlock substitute to bury. If the camera panned away at the key moment, not all that much handwavium needed - at least not by standards of this series.

a heck of a lot more to them than feeding them twice a day

I've known plenty of people who "just feed them twice a day". If that. It's called Jamaica.

How tall was the building he's supposed to have jumped off of? This episode turns out to be the only one I don't have.

But if you are fighting boredom, you probably don't take the low maintenance path to pet keeping.

And the building looked about ten stories to me.

The building was St. Bart's. It's four stories tall.

But if you are fighting boredom, you probably don't take the low maintenance path to pet keeping.

You're trying to apply "ease of use" to good "life choices" for a psychopath. I don't see how what's easy is at all relevant. But I wanted to point out that sustaining animal life doesn't have to be challenging--you are setting arbitrary constraints on what that life consists of. You might not be spending time doing complex poodle cuts, but to Moriarty petting a dog and making topiary of its hair might be equally boring.

Getting reward out of suffering is a thing in and of itself, and trying to substitute for it based on a hierarchy of difficulty is a radical oversimplification of human psychology.

It may be possible to survive such a fall through landing on your feet, but you'd have significant ankle injuries. Now, we don't know how long the graveyard was after the fall, but he really didn't give that impression.

What we saw: Sherlock falling facing away from the building, so he'd be perpendicular to the walkway. Sherlock landing (well, sort of. We don't see him hit, but we hear it) (seemingly from a pretty short height, really) with his body parallel to the walkway.

How much time passed between those two shots, we don't know. Also, John did not see him hit, either. There was an outbuilding and a laundry truck in the way.

I...may have been having this conversation for a few months now.