Was genuinely surprised how they adapted that in 'Breaking Dawn Part 2'. The whole climactic battle is a big vision sequence, right? It's not real. So in the 'movie', from a viewer's perspective, a ton of characters die. You see Alice take Jane's head off, Carlisle gets decapitated by Aro, it's brutal. But then it reverses, because it was just a possible future Aro was seeing. So the only actual death in the movie is Aro himself, when Bella uses her shield power to hold him still and Edward beheads him. I remember the theater gasped during the fake-out deaths, especially Carlisle's. It was a clever way to raise the stakes without messing up the book's ending where basically everyone lives.
Some people thought it was cheap, but I thought it was a decent cinematic solution. The book's final confrontation is all talk, which doesn't film well. The fake battle gave them a way to show off everyone's powers and have some action, then pull it back. So yeah, final body count: one vampire emperor.