Only God knows the answer to that question; and God ain't telling, as my old dad would say.
Then how do ordinary christians know if they are redeemed? What you suggest is a gamble for believers.
However, in John Milton's Paradise Lost, even Satan has the opportunity to repent, and all eternity in which to do so. This requires him to sincerely and humbly take the knee before God, which his pride will not allow him to do.
Is Milton's work part of the Bible now? Is he authoritative?
This whole idea is kind and compassionate, but still, is it justice? A guy is a murderer for most of his life, and then when the end nears he suddenly sees the light? Sounds self-serving. Even if sincere, the sinner had the chance to be moral sooner, but rejected those opportunities for more self-serving goals.
So Hitler repents, is saved, and goes to heaven. No punishment? Killers who get caught and convicted are sent to prison, even if they repent and show remorse for their actions.
This is another scenario where Christianity is too idealistic, and too binary. Is heaven really an option for killers even if they repent at the end? Catholics had Limbo for the souls of children who died, but they got rid of it some years ago because it was not a fan favorite by parents of dead kids. But that wasn't a bad idea if they had only used Limbo for those on the bubble.
The whole point of hell being a threat is that believers would really think it exists, and they would adjust their behavior to avoid it. But as we see some religious leaders adjused the interpretation of the Bible to include immoral acts. like executing people for witchraft, lying about science as the creationists do, evangelicals who are bigots and racists, the whole prosperity movement which is nothing more than an excuse for the sin of greed, etc. Christianity is a catastrophe of "truth" with no set morals and ethics. It is "anything goes theology". Think you're going to heaven? If you say so.
