Death in the sense in which it's tragic at least in the aspect of being a permanent separation of someone whose very identity is intertwined with our own. Whatever may be meant by Death forever being undone, I assume that St Paul has at least this in mind.
Certainty should be tabled by everyone. Let's all rather show humility. So, St Augustine seems certain that Hell will be well-occupied and will be forever and inescapable. By contrast, David Bentley Hart argues as if he's certain that all will be saved in the end. Most of us (hopefully) are in between these two extremes of certainty. This in-between is the most reasonable space to occupy, given the ambiguity of scripture and the finitude of our own minds (and other matters like the nature of God, the nature of love, the nature of humanity, etc).
Properly speaking, God is not actually longsuffering (meaning, Oxford: "having or showing patience in spite of troubles, especially those caused by other people"). Patience necessitates finitude. It's a virtue for humans because we do not know how things will turn out. But for God who is infinite in knowledge and power, patience is not possible. This is anthropomorphic speech.
Here is the verse again: "For this we toil and struggle, because we have set our hope on the living God, who is the savior of all, especially of those who believe" - 1 Tim 4:10. You are theologizing this verse because of your prior commitment to the eternal separation of humans in the afterlife. The straightforward reading of the line suggests that God is everyone's actual savior, but God is especially the savior of those who believe.
Attempting to parse it out ("offer of salvation" & "those who have accepted that offer") is theology. I'm not saying that theologizing the scriptures is illegitimate. It's perfectly fine. It's a way to attempt to get the ambiguities of the NT to all fit together in an overall coherent framework. But, let's not pretend that you're simply reading the text for what it's saying. You're inserting your eschatological vision into it and reading it through that lens. St Paul could have easily enough said here what you're saying--that the offer of salvation was given to everyone, but God will only save those who accept that offer. But, he doesn't say that. He says that God "is the savior of all, especially of those who believe."
There is nothing particularly strange about inequality in the outcome of Heaven. In fact, Christ's language would seem to suggest inequality in the hereafter (the last will be first, and the first last). St Paul, in another letter, says, "So then, while we have the opportunity, let us do good to all, but especially to those who belong to the family of the faith." - Gal 6:10. We do good to everyone (and yes, that means every single one) but especially to believers. I fail to see the problem here. You seem to be suggesting that one group of humanity being special is somehow an issue.
I don't know what you mean by this, but there is enough ambiguity within the NT that a great many fathers of the church were open to the possibility of universalism (or were explicit universalists). There is only one place in the gospels when Christ is directly asked if few will be saved (Luke 13:23), and he does not answer this question. If the answer were so clear, as you'd like to believe, stands to reason that his answer would have simply been "yes" followed by whatever other guidance he wanted to give. But, there was no yes in response to that question. There wasn't a "no" either. There was redirection to what we ought to be concerned about--the narrow gate.
Lastly, I'm not countering your suggestions that Matthew 7 and John 3 advocate eternal-separation because I see no reason to. As far as I can tell, you haven't made a case that those verses have anything to do with the topic.