Jesus Will Return Once the Whole World has Heard the Gospel
Matthew 24:14 And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
Many take Matthew 24:14 the wrong way. They think Jesus will not come back until that ONE person has finally shared the gospel with that one unreached people group who has never heard the gospel.
People don't realize God's name is Jealous. Exodus 34:14 for thou shalt worship no other god: for the Lord, whose name is Jealous, is a jealous God...
God will receive ALL glory for EVERY THING. There won't be a single man to receive the glory for being the last person to reach the last unreached person with the gospel.
How do I know that?
Revelation 14:6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people, 7 saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters.
God will be the One who makes sure the gospel is preached to every last person. Nobody will get the glory for doing that.
By the way, the person who wrote the 'answer' on GotQuestions.org got it wrong. God is the one who is accountable for every person who wants to hear the Gospel. There isn't anybody on earth who will not hear the Gospel who wants to hear it. Oh! But, nobody wants to hear it! God knows the heart and he knows who will hear it if they are given the gospel.