Plum,
You wrote: [The Bible says] "This good news of the Kingdom will be preached through out all the inhabited earth for a witness to all the nations AND THEN the end will come." ... So before the end will come, everyone must here the word of God.
First of all, I don't even think JWs teach that. When asked how the end could possibly come soon since billions of people in lands like China and India have never heard the JW good news they use words like "community responsibility" to explain why it may not be necessary for every individual to hear their preaching.
You may also want to read the context of Christ's words. In verse 14 we find that He said what you quoted Him as saying. However, His words which immediately followed, those recorded in verses 15 and 16, make it clear He was actually referring to a work which would be done prior to the time Rome destroyed Jerusalem in AD 70. Christ's words in context are these: 14: "And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come. 15: So when you see standing in the holy place 'the abomination that causes desolation,' spoken of through the prophet Daniel--let the reader understand-- 16: then let those who are in Judea flee to the mountains."
Paul makes it clear in Col. 1:23 that he considered Christ's words spoken in Matt. 24:14 to have already been fulfilled in his day. (Colossians was written before Jerusalem's destruction.) To the Colossians Paul wrote, "This is the gospel that you heard and that has been proclaimed to every creature under heaven." Now we know that at the time Paul wrote those words the good news of Jesus Christ had not yet been preached in "inhabited" places such as North America and Austraila. So, Paul must have understood Jesus' prophecy of a worldwide preaching work, and his words describing the completion of such a work, to refer to a work that had been done in "all the nations" then known to Christ's apostles to whom He spoke the words recorded in Mathew 24:14.
With such things in mind we have no reason to believe that it is biblically required that everyone on earth must hear the good news of Jesus Christ before He returns. If this understanding is correct, that Christ is returning to judge only the Christian world, then Christians, who all have the same "one hope," will then have plenty of people to rule over as they serve as kings with Christ for 1,000 years. And they will also then have plenty of people to help come to know the true God as they serve as His "priests." For that is, after all, what priests do.
The Bible does not tell us exactly what will happen in the future. Because it does not, the beliefs of Jehovah's Witnesses and my beliefs on this subject matter, which I have just presented, can only be considered speculation. However, I believe that Jehovah's Witnesses should be made aware that there are other ways to understand God's clearly stated intentions to have the meek inherit the earth (Ps. 37:11), and His intentions to have all Christians rule with Christ for 1,000 years, than to change the good news preached by the apostles which offered the same "one hope" to all Christians. (Eph.4:4-6; Gal.1:8,9)