I'd say that refocusing on the question, which is about the intent of the author and what the writer is saying, the answer I'd give is that no good literary theorist would say that they 100% know for sure what the author intended.
I can't read a text and say "This is definitely how the author wanted this to read".... unless I guess the author is J K Rowling and can spend basically all day filling in every gap with what she wants you to know she intended (even if it actively contradicts what's in the text or things she's said previously) or George Lucas, who will go back and tweak his movies if he gets the slightest idea that somebody has understood them in a way he doesn't like. But even these two are unreliable narrators about their own past intent. Rowling says she never explicitly saw Hermione is white, which contradicts evidence like her own drawings of the character and other pieces of past evidence, rather than saying she changed her mind having seen the appeal of a black Hermione when other people pointed it out, basically trying to retcon her past self's intent instead of admitting times have changed and her mind was changed about her own work. Lucas went back and infamously changed a scene in Star Wars so that Han dodged Greedo's shot and then shot second with weird, scrappy editing. If at the time he'd actually wanted Han to shoot second, he'd surely have made that change while shooting, or even removed the shooting part altogether if the shot was ruining the character and none of the footage worked. Lucas changed his mind about how he wanted people to read the scene and tried to retcon what he said his intent was.
(Side note, an example of a writer not doing this is Ursula K Le Guin, who openly acknowledged that she had changed her mind about how she thought about women in the past when writing female magic casters as inferior and wicked in the early Earthsea books over the years since writing them, and wanted to do them justice in further books in the series).
What the author intended as the meaning of a text and how it can be read are two things which an author can really just hope overlap. You can believe that a character's death redeems them all you want; your readers don't have to agree.
Bringing things back to the transphobic queen of TMI herself, J K Rowling is very explicit on the fact that she sees Snape's death as a redemption. To her, he did it for love, was redeemed by love and Harry recognised that redemptive sacrifice and named one of his kids after him. Because she's been so insistent about it, we can be pretty sure that in the spirit of your question, she wanted him to die and that dying redeemed him. Although we don't know if that's what she feels is the only way to redeem him, but it's hard to find a writer who says "this is the only way I could have written this scene".
Let's assume that Rowling believes that Snape dying is the best possible way to end Snape's arc. That him falling in love with somebody else and realising he's been a dick for years agonising over Lilly as if because she was the only person who was nice to him as a kid that left him thinking she was the only nice person in the world, and on realising this becoming a better teacher and perhaps even a caring adopted father to the orphaned son of Lupin (somebody he used to hate), was something she realised was a possibility, but decided "no. The only way for Snape to be redeemed is for him to make one final sacrifice for Lilly's son to show just how much he loved Lilly, showing that because he loved Lilly, he actually wasn't an awful guy like Voldemort, who was completely incapable of love". Even if she believes that, it doesn't necessarily mean it's correct. Readers and critics are allowed to then examine Rowling's choice there and to go, "ummmm.... lusting after a woman who you bullied for years and killing yourself to prove that doesn't really redeem you from years of working for the super evil murder wizard, or that you were awful and cruel to your students to the point that one of them saw you as his literal worst nightmare." and to consider what the fact that she chose this outcome and frames it as a redemption in her text as well as explicitly saying outside the text that she sees it as one, says about Rowling's beliefs about people.
So yeah... basically it's messy, and even if the writer did see it as the only outcome that can possibly work, it doesn't mean that the reader will agree, and it's possible the author's mind will change over time about it. In my experience though, most writers don't consider their choice the only possible choice, but the best choice for the story they're telling. I've killed off characters in stories in the past because it seemed like the only way to resolve their plot at the time, only to find that as I improved as a writer, it really wasn't, it was just a quick and easy way and didn't really fit their narrative arc at all and I was thinking in way too rigid a way.
