Can you kill important characters? Sure. Happens all the time.
Should you? When does that work and when does it fail, or perhaps go over the top? Let’s take a look at various examples of SFF novels featuring the deaths of important secondary characters and/or the deaths of protagonists, and consider why those do or don’t work.
As it happens, I’m not personally too keen on authors who slaughter characters left and right for no good reason. I’m thinking here of Game of Thrones. It was one thing when Martin set the reader up to think Ned Stark was going to be an important protagonist and then killed the character early in the series. That was a way to break important assumptions for how the story was going to unfold. It increased tension in a good way, for a good reason — who else might seem too crucial to die, while actually headed for an early grave?
But besides that, as I recall, from time to time Martin also introduces a new pov character and then kills that character at the end of the chapter. I mean, what is even the point?
On a related note, personally, except in murder mysteries, I detest the trick where the author kills the pov character with whom he opens the book. When that happens with a new-to-me author, it’s probably going to be a DNF moment.
Even more annoying than that are authors who set out to manipulate you by introducing a very likable character specifically in order to kill her. (It’s always a “her.”) If this manipulation is too blatant, it’s a real turnoff. I’m thinking of all of Steven King’s recent books, here, where very likable characters are obviously present solely to function as tearjerkers upon their gratuitous deaths, which is why I eventually stopped reading King’s books.
However, it’s not like I’m opposed to character death per se. The pathos created by a sympathetic character’s death can be very useful when it’s done well and for a good reason. In a recent WIP, I deliberately killed a particular secondary character after going to some trouble to make the reader like him. Even though his death wasn’t at all important to the plot, it wasn’t gratuitous either; on the contrary, it was essential. I had to do it because without the death of that character, the deaths of a couple hundred other people would have passed without a blip on the reader’s emotional radar. They weren’t known, they were just a faceless mass. The death of the one character served as a proxy for all those deaths, giving that whole scene emotional heft it had completely lacked before.
I’ve killed other characters, of course, and I’m sure I’ll kill more in the future. Sometimes it’s necessary to get the plot to work and sometimes it’s necessary to add emotional weight and sometimes for some other reason — you know, there’s an infographic for this — here:
I think this is a very good infographic! Best touch: having “removes an extraneous character” on both sides of the graphic.
Perhaps somewhat iffy: while the death of a secondary character may be motivating to your primary protagonist, the modern author may wish to avoid having all the female characters exist solely to motivate the male protagonist through their abuse and/or death.
I will also just note, considering the above infographic, that if I’d known how The Great Escape ended, I probably wouldn’t have watched it. I prefer less realism and more survival in my WWII fictionalized novels and movies.
But, though I really like the above infographic, I believe that the whole thing can be boiled down to this: two things are always, always bad when killing a character —
a) The reader can see the strings you’re pulling. You should indeed do things for a reason, but your manipulation should not be nearly that visible.
b) Killing a dog. Sorry. Other sympathetic characters may have to die, but the dog should live happily ever after.
Incidentally, T. Kingfisher’s The Twisted Ones, which I’m about a quarter of the way through now, features a Very Good Dog. The dog is an important character AND important to the plot AND really well done, because Ursula Vernon / T. Kingfisher knows her dogs.
And right up near the beginning, the author makes it clear that the dog lives by throwing in a casual line: “… but because he’s a coonhound and all nose, we both survived.” or something like that. I bet that is not a chance occurrence. I bet she deliberately chose to let the reader know this up front, to avoid alienating those readers who won’t touch a book until they can be sure the dog lives.
I really like the story so far, by the way! Getting creepy, but without overt gore or anything of the kind. It reminds me just a bit of Sunshine by McKinley, even though it’s very different.