@akargeI've told this tale before but … in one post-apocalyptic series, I decided to kill every single character at the conclusion of the first of a three-novel series. The key is, the only way to pull of anything that extreme, you have to make ALL the characters fascinating, so rather than some minor tertiary character, everyone who dies must rip the reader's heart, as losing a favored character, regardless of their role, is a heart-breaking experience.
Yet due to that extra character development, my 'experiment' paid off in spades. Except, roughly a third a readers couldn't finish the first book, while the second third hated the story yet read it anyway, while the final third were SO captivated, they loved the story despite the many dead favorite characters.
However, whether the finished the first book, they ALL returned for the second, and the whole series ended up being one of my highest rated. The caveat to this—and there's always a caveat to these types of stories—is that the two protagonists who were the last to die in the concluding chapter, wake up again in the epilogue—which accounts for what happens after the story concludes. And thus, in the sequel, they learn that they've acquired immunity to the all-pervasive plague, which they spread as best they can, a single person at a time—treating one then leaving them behind to then treat everyone else surviving in the region.
And such a premise is literary gold, all due to the extra investment if extra character development for ALL the characters, however minor. Thus the protagonists remained the central protagonists, yet each survivor also became protagonists in they own lives.
Still, that's a technique you can ONLY use once, before it becomes hopelessly tiresome. As once readers anticipate characters are dying, they'll then know precisely what to expect, so in the sequels, they each died one at a time, in isolation not in large numbers. A typical reversal of expectations, so the continual deaths are simply teasers.