This is a huge issue, beyond the understanding of you or I (thankfully). I would hate to know which of my friends will not be with me in heaven. Fortunately, God is 100% capable of making the right call, and you can bet He will do so. That means you and I don't have to.
I am certain that Jesus Christ spoke truthfully when he said, "I am the Way, and the Truth, and the Light. No one comes to Father but by me." That sounds simple, but there is a lot to it.
You might check out what C.S. Lewis had to say on the matter. Lewis gives an example in the last book of the "Chronicles of Narnia" of a situation where, at death, unbelievers who nevertheless belong in the Kingdom of God have a chance to see Jesus Christ. Most cannot bear to look, but a few can. They are overcome with grief at their now manifest sin, and ask for forgiveness. They know full well they do not deserve it, but Jesus Christ grants it anyway. Lewis gives other examples in other books as well.
One danger in this line of thinking is that non-Christians somehow have an escape clause. They can always make up their mind later. Not so. The Bible refers to these people as fools. God defines "later", and He always gets it right. In my opinion, willfully delaying the decision, once the right opportunity comes to you, is the biggest mistake you can make.
Bottom Line: God knows His sheep, and He will not lose a single one. I know I am one of 'em, and I have hopes for those I love. Even the ones that seem pretty far from saved.
They will say unto the Lord: "Did I not prophacy in your name? Did I not drive out demons?"
The Lord will say : "Go away from me, for I never knew you."
If the Lord rejects those who minister but are without faith, why would he take pagans who did nothing in his name but condemn his teachings?