Um, here's a thought, but don't read it unless you've already read the book, okay:

I feel kinda horrible to say it, but I was kinda glad when Miller got killed off. Not that I wasn't sad; he was one of my favorite characters, and I really loved how he developed over the course of the novel. It's just like this: if I'm going to stick around for a what, nine-book series, I want to see that the authors aren't afraid of change. Too many books I've read are afraid to let anything happen because they want their readers to keep loving the characters they first saw. (The Oz series is predominantly on my mind; every book solved the conflict with yet another magic object to the point where one of the later plots--and in my opinion one of the more interesting ones--has an evil magician steal all their magic stuff, so they have to work without. I mean, seriously: how can you keep a story interesting when one character has a belt that lets them do literally anything?)

Anyway, by killing Miller, the authors have convinced me that they're going to do what's right to make an interesting story, even if it hurts the reader's feelings a bit. And that's all right. In fact, I much prefer that to static characters. I don't want a bunch of novels with practically identical plots. (I'm talking to you, Sherlock Holmes and Hardy Boys.)

And to those who have read further into the series (preferably until Cibola Burn):

Yes, I realize Miller came back. My point stands; he definitely was extremely changed and arguably not even the original person at all.