Christians can judge actions, or lack of action, yet to judge motives is something we cannot do.
Yes, repentance is key to salvation,but you don´t repent to me, you repent to God.
Here is truth that many refuse to accept.
We are all sinners, every one with no exception. Your sins, whatever they are, are no worse than mine, we are all in the same boat on that score.
We are totally estranged from God, for He despises sin. But we have an intercessor who solved the sin problem for us, as our substitute He payed the penalty for our sin, and lived a perfect life as our substitute, so we can be seen as sinless by God through him.
Repentance simply means making a conscious choice to turn away from our sin. To work to over come it, not to be saved, but because we are saved.
Now to your question. It appears that one who does not accept the intercession of Christ, will be lost in their sin. Notice I said appears, one is going on in their mind, if anything, between God and they is totally unknown to me, I can say nothing for sure about the disposition of their soul.
We know that God is perfectly just, and perfectly merciful.
Knowing that I have often wondered about, say an African 500 years ago deep in the interior of the continent. He is a good man , kind, loving, merciful, sharing, all the attributes a Christian should have, yet he knows nothing of Christ , will he be lost ? I haven´t a clue.
What I do know is that in Godś mercy and justice, things will be as they should.