What about the people that never hear the Gospel and or no missionary ever visits them and shares the Word about Jesus and how there's no other way to heaven except through Jesus Christ. What happens to these people when they meet their maker and try to explain to God that it wasn't fair that they can't enter since nobody ever explained to them the Gospel?
Your questions rest upon assumptions about God's judgment and man's arguments that you might want to reconsider. Complaints against God's unfairness are not only bogus they are formed in man's biased, self-righteous judgments and perceptions. The idea that anyone is really going to be presenting explanations and/or excuses "when they meet their maker" is a delusion built upon one's own system of accusations and excuses. After all, those who offer up explanations regarding fairness or unfairness do so according to fleshly judgments. Bear with me as I share what has come to mind (i.e. "ramble on") from having considered these questions, okay? :)
Now we know that whatever the Law says, it speaks to those who are under the Law, so that every mouth may be closed and all the world may become accountable to God; because by the works of the Law no flesh will be justified in His sight; for through the Law comes the knowledge of sin. Romans 3:19-20
If with all the expertise of the law those under it have their mouths closed then there is no possible way that ANY explanations will be heard before God by anybody else. The conclusion against those under law has made an iron-clad nullification against any and all defenses. We've really got to get past the idea that any will stand before God with explanations or excuses.
Many will say to Me on that day, 'Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?' And then I will declare to them, 'I never knew you; DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.' Matthew 7:22-23
Somehow we have mistaken Jesus' confrontation with the religious mind and instead turned it into some kind of a preview of a yet-to-be-released movie. The truth is that Jesus was speaking of God's judgment regarding the reality of their current self-righteous perceptions and imaginations. He was exposing the "lawlessness" of the religious self-righteous man under law and making this declaration known before Israel.
Honestly, I think we project our own doubts, fears and insecurities by posing questions built upon false assumptions of God and his judgment ... and his mercy. I think we're trying to figure out how and why God can do what he does without being unfair, for if we were to be honest we'd have to admit that we still think he is unfair. Maybe we're also trying to cover our sense of guilt and failure, as we have not been able to convince all the people we thought we'd be able to convince about Christ.
I find it quite interesting that Paul had addressed a very similar question in Romans 10 - only here it was regarding God's people who had rejected Christ - where we usually hear a sermon preached about the need of a preacher if one is to hear. And from this many missionaries have been sent under the pretense that without a preacher the message could not go out. And yet, Paul continued on with a different consideration long before we made our own religious conclusions that have motivated so many.
But I say, surely they have never heard, have they? Indeed they have;... Romans 10:18
Through all of this Paul makes a continued insistence of the grace of God that is not dependent upon man's decisions and choices. Instead, it is demanded that grace has come to those who had not searched for it. God's grace and mercy is not confined nor limited by our inadequacies or false beliefs, and his reach is not hindered by that which opposes it or by those who reject it. Trust him!