Saddened to hear of the loss of your nephew. It's heartbreaking. Even more so, the desire of your heart for his eternal destiny.
My father passed away ten years ago, and never communicated or acknowledged, to my knowledge, a belief in Christ. Yet, in the process of his dying (he had metastasized prostate cancer, so it took awhile), I saw a softness in his attitude, a gratitude for his family around him. My wife shared with him that we were all praying for him, and he said, "I don't need prayer. I am full of thankfulness." Where does that come from, in a man facing pain and sure death, who never acknowledged the saving work of Christ? He was obviously touched by grace. After he passed, I had vivid dreams about him, actually visited with him, and he was in a place that was a replica of our home, but bathed in a brilliant light. He was just going about his business, fixing the fence, working in the garden. I came to realize that what I had been taught in my 40 years in evangelical churches may not completely be correct or complete about God's plan and dealing with the supposedly "unsaved."
A turning point in my understanding came as a men's group I was in studied through Romans. Let me share the passage which shook my "informed evangelical" understanding: Rom. 5:12-21. Note the scope of Adam's sin, and the scope of Christ's "one act of righteousness" (see v. 18, specifically). If Adam's sin resulted in the condemnation of all persons, the work of Christ resulted in the justification of "all men." Unless "all" doesn't mean "all" (as I've heard some Christians argue), there is hope for all, even my father; even your nephew. That's where I started. Our pastor, who led the men's study in Romans, said in response to my observation of Adam's vs. Christ's work that, "Well, if all we had was this passage, we would have to conclude that the death of Christ reconciles all to God. But read the rest of the New Testament to see what is said about the destiny of the unbeliever." And I did that. I read a new, clean, copy of the New Testament, underlining verses which speak of a future punishment in red, and which seem to speak of a universal salvation in green. I'll tell you, while there are some "red" verses, the overwhelming number of verses underlined in green was an eye-opener.
Also, look at Rom. 5:10. "For if while we were enemies, we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved [the Amp. NT translates "saved" as "daily delivered from sin's dominion"]." Who did Christ die for? I think the Bible clearly says "the world" -- everyone. It sounds to me that Rom. 5:10 is saying that "all, everyone," are reconciled to God through the death of His Son. And that "salvation" isn't simply getting out of hell and into heaven, but is a daily experience of the grace of God and victory over our flesh, the world, and the devil through the power of the indwelling Christ.
This is a huge doctrinal leap, and I would not expect you to accept it based on my brief post. But consider it, and open your heart to the possibility that God's mercy is greater than anything we can imagine, greater than anything we've been told in the evangelical church. I have immense hope for your nephew. Jesus went to infinite lengths to die for your nephew. Why wouldn't He continue to go to infinite lengths to wrap your nephew in His arms at that very last moment?
God bless you.