It may help to define what it means to qualify for redemption. @Adeca set up one of their own with excellent side questions.
So what makes a character become irredeemable for me? Sometimes I despise a character that isn't "evil" in the sense of their world, or other readers. They just did something that to my values now regards them as disgusting. For them to start re dreaming themselves one of two things have to happen:
1) They realise that it wasn't ok and try to get better
2) The event/action is re-contextualized
It sounds like for a lot of people in this thread, #1 is the defining line. However as Adeca brought up this can get blurred with worlds with the un/living able to interact with each other. In those worlds, I almost want to say the character isn't truly "dead". Death, normally, implies a lack of being able to make new memories with the deceased. However if you have a setting where souls remember their past lives and can do actions to others- then they aren't really "dead and gone". Their character is still allowed to develop.
Number 2 has nothing to do with character development and is all about reader information. You've deliberately set a character to look one way and then reveal their "true form" later. I can understand why others wouldn't think that those count as redemption, because the reader wasn't allowed to properly judge a character. But first impressions can really stick. For some, that will never be enough. For others, perhaps they can acknowledge that the situation was greyer than known before, but everyone has lines to were what kind of context is enough for certain kinds of actions.
What can muddy the waters further, @darthmongoose bring about a big pet peeve of mine! If you know you have a character, no matter how precious they are to you, do not make the narrator (at least those that are in the 3rd person omniscient sorts (1st person is fine because they are an actual character)) SIDE with anyone. That defeats the entire important part of why you use that narrative unless its purposely there to make people question it as well. In the end it should be up to the reader if this character is redeemed just as much as its up to the reader to who their favourite character is. I don't like being told how I should feel about someone.
And to @amortelito, that is more cultural thing. Not all people get a free pass upon their death. I'm sorry you are made to feel guilty about feeling negative towards those who have hurt you.