I'm fortunate so far, in that I've yet to get any significant pushback on killing any characters in my books. To which I saw: wait for Imposters of Aventil.
(Because I'm not entirely truthful about no blowback-- there's something there that one of my betas found devastating.)
I tend not to be the "let's be horrible to my characters" kind of writer. Not out of any specific gentleness-- deaths and serious injury are abound. But I think you need to make those moments matter, and therefore you can't cheapen it too much with frequency.
Or, rather, you need to set a tone. If the tone is set at "Horror", then you've got to kill characters left and right. That's what Horror is supposed to be: a setting where You Will Not Survive is the default that characters have to work out of.
I write Fantasy Adventure books where the tone is equivalent to, say, the superhero shows on the CW. Each one has it's own specific rules about killing and death, of course, and as the writer I have to respect that tone.
By which I mean, it's not just about if characters die, it's how my characters approach lethal force. To continue the CW parallels:
- Veranix in the Thorn books is closest to Arrow, in that using lethal force isn't necessarily an ideal, but it's also not off the table. Sometimes the situation will-- in Veranix's mind-- render it necessary. He's out there in life-or-death fights, so he can't hold back in the moment.
- Minox and Satrine in the Maradaine Constabulary are closest to The Flash. They serve as officers of the law, and so their mandate is a clean arrest and proper justice. They strive to do things the "right" way, bring someone in alive. That doesn't mean that lethal force never happens, and they don't struggle with it... but they take it very seriously. Also, most of the time the people who die in these stories start out dead to begin with.
- Asti, Verci and the rest of the Holver Alley Crew of the Streets of Maradaine are closest to Legends of Tomorrow, in that between their darker pasts and operating outside of the system, they don't hesitate at lethal force when the situation calls for it. They're anti-heroes who do what they have to.
- Finally, Dayne of the (hopefully) upcoming Maradaine Elite series is very much Supergirl. That's all I'll say about him for now.
Hopefully, when a beloved character does get killed (perhaps in Imposters of Aventil, now available for pre-order?), you'll understand the brave and bold choices I've made there.