How are you using "saved"? Are all your instances in this section about the afterlife only? If not, then there is something presently saved in a Christian that can be undone in some capacity.
I'm not sure what you mean by something presently saved that can be undone.
As far as the problem with saying will, being that it would require knowing the person was a genuine believer, I don't think this is fair to the new testament. The texts repeatedly testifies to watching out for false teachers, describing their character and testing what they say with Scripture. For this reason I don't think measuring out a punishment has room for suspecting who is genuine.
I think the question revolves around how we treat the words, spoken or written by fully human saints of the bible.
Do we treat their words as golden, uninfluenced by human frailty as we would the direct word from God, and also Jesus in human form? Or words that are messages from God, spoken or written along with human influence?
An example would be the words from Paul to the Corinthians that if he had it his way, all Christian men would be single. This was a very admiral statement. Even a Godly statement. And the reason is that Paul wanted to see Christian men completely free to serve God without the distractions of marriage.
However, it's not something that Jesus/God would suggest because if every man on earth became a believer after Pentecost and remained celibate, there would be no
reproduction, and humans would die out.
Another example.
Sometimes prophets spoke the direct word of God without their humanity manifesting itself. And sometimes they said things very human. The prophet Nathan was fairly straight forward when he gave God's message to King David concerning the sin involving Bathsheba. But even there he qualified his prophesy by giving the king a scenario so that David could better relate to the prophesy. And Nathan probably did that because he wanted to be tactful, thinking that the king might not respond very well to just being told that he sinned. That was Nathan's human side if that's the case. Obviously God wouldn't worry about any retaliation when giving a straight forward message.
Did Paul have the same kind of insight Jesus had about the condition of another person's soul? Jesus could tell for instance that the thief on the cross would be with him in paradise. Paul on the other hand probably had a realization that the chaff could appear like the wheat. And unless he had an accurate direct revelation from God, there had to be that room for error no matter how slight. He at times spoke with positive affirmation, stating he had confidence that God would see believers like the Philippians into his kingdom. But that still leaves room for sleight doubt because he understood it's not guaranteed. Like when we tell some we know they will succeed, we have to leave room for error even though we are expressing absolute confidence because we know the possibility of failure is still there. We can't say they can't fail even if they tried to because the affirming word is not a physical law disallowing failure.
So if we ponder Paul's words allowing for his humanness to manifest, then I don't see any real problem with what I said. But if the bible only records the word's of Paul that are divine without human influence, then that's another story.
I think the text suggests that Paul may have had doubts about the person's stance as a believer.
Why?
Well Paul did make judgments about the condition of some follower's soul as not being genuine believers when he referred to those who left them. Paul considered them as those who were never of them. And if they were, they never would have left. And these were those who had fellowship with believers living under persecution, like those Jesus referred to when giving the parable of the sower.
So Paul may have viewed the man in sin positively to some degree because at least he didn't actually leave the fellowship.
However, there may have been some doubt because this was in Corinth, where a Christian could probably have had one foot in the church, and the other in the world.