Basically the deaths of everyone.
After this, there's a long section in which
Tirian, Jill, Eustace, and others explore the "New Narnia", ending up at Aslan's country.
That last bit is one of my favourite parts of the series, a beautiful picture of the peace after the destruction on earth, and a glimpse into Lewis's own theology.
Now, imagine this in film. The big climax, dark movie leads to a dark climax, and then it's literally all sunshine and roses. I'm not sure lots of people would enjoy that. Similar to Lord of the Rings, where the climax is the destruction of the Ring (I doubt I need to "spoiler" that), the filmmakers opted to remove the canonical conclusion of the scouring of the Shire, a wise decision in my opinion.
I wonder what the best way to do LB would be. As much as I think film studios are trying to squeeze money out of their franchises, I wonder if a "Last Battle Part 1" and "Last Battle Part 2" would be a decent idea. In sort of the same split as the last two Hobbit movies, finish one movie part way through the drawn-out climax (Tirian and the others fight more than once, maybe leave some sort of cliff-hanger?) and then begin the second movie with the literal LAST battle.
Or maybe the better option is to leave out some of the detail of the
exploration of the New Narnia
Any thoughts?