That’s a good question, IF you don't understand how our Creator has chosen to communicate with us. And because He HAS chosen to communicate the reality of His existence to us, we don't need to worry about some people “failing to get the message.”
First of all, God is Love and God is Just. No one who should be in heaven will miss the opportunity. That is an absolute fact.
Second, there isn't a single person on this earth who doesn't know about Creator God. We know about His existence through the existence of the universe and the whispering of our conscience, which is the presence of The Law that is written on our heart.
Whether it's a baby like John the Baptizer leaping for joy in the womb of his mother Elizabeth, or an ancient man from an unknown tribe in a tropical jungle giving thanks for his catch of fish, or an atheist furiously pounding away on his computer explaining why s/he has rejected the evidence for God, each and every one of us responds in some way to the existence of our Creator.
The degree of our awareness may vary but each of us knows. Abraham communicated directly with God. Rahab the prostitute barely heard of Him at all. Neither of these people knew Jesus as we know Him, but they believed God and were counted as righteous because of the way they responded to the knowledge of God that they did have. Those who have little information will not be expected to respond like those of us in the West. “To whom much is given, much is required.”
Fact: No one exists who isn't exposed to the evidence and reality of our Creator.
Psalm 19:1,2 - The heavens declare the creative glory of God; the enormity of the universe proclaims the ability of what He is able to do. Day after day the cosmos pours forth a description of Creator God's power and intellect; night after night it reveals the knowledge required to produce a life-sustaining, mathematically precise, moral universe.
This knowledge of God's existence is not limited to one country, one society, one culture, one language group, or one time in history. The knowledge of God's existence is available to every single person on the face of the earth from the beginning of time until its end.
What's more, all of us know God's Law, the purpose of which is to highlight to us our need for salvation. Either because we live in a place like the West where we've been exposed to Law in written form, or like everyone else on the planet, all of us know the “Law” in our heart of hearts. We know whether we are wilfully obeying or disobeying our conscience. The more we obey God the more of Himself / Jesus reveals to us.
A good friend was telling us on Sunday about his work, many years ago, translating the Bible for a remote population in Papua New Guinea. For these people, at that time, attaining the level of “bronze age” would have been a step up. Stone-age would have more accurately described their living situation. As they were speaking about Genesis 1:1 - “In the beginning, God created the universe,” the tribal chief scoffed when my friend told him that some people in the modern world had a hard time accepting the idea of a Creator. Unknowingly stating a scientific fact that modern atheists refuse to accept, this virtual stone-age tribesman emphatically said, “Everything that begins to exist has a cause. Of course this world had a Creator.”
There isn't anyone on this planet that can't know that God exists. Through the evidence of creation, everyone at some level knows of Creator God. From the evidence of our conscience, each of us knows we need forgiveness. From the evidence of our inability to live up to even our own standard of moral conduct, each of us knows we need a Saviour. God Himself promises that if we examine and follow the evidence given to us, and diligently search for Him, He will allow Himself to be found by us.
Good luck on your journey.