A television series may keep the fans on edge by killing off favorite characters. Think Game of Thrones. I'm still upset over Ned Stark's violent demise. No, I didn't read the books. I tried but they are huge and the paperbacks have tiny, tiny print.
Unless you're actually writing a series of book, you don't have the time to develop beloved characters. I remember a well known romantic suspense author saying she upset some of her readers when a dog was badly injured. No one gave her grief about the kid in danger, but don't hurt the dog.
An author walks a tight line by endangering a well known character. I suppose an author of a long running series might get tired of a character. Even Agatha Christie didn't care for Poirot. She was quoted as wondering why she ever "invented this detestable, bombastic, tiresome little creature?"
It's scary. You risk losing a reader if you've developed a fictional character and suddenly they are gone. Does this development make sense? Is it really necessary? Does it take the protagonists in a different direction? Be ready to answer these questions and convince your readers you haven't lost your mind.