Technically the Christian message has been preached to the four corners of the earth (not the Watchtower message, but that is not the gospel) if one factors in the broad reach of the Internet, radio and Television, not to mention over 2 billion Christians. And then the end will come.
http://www.144000.110mb.com/directory/607_bce_586_587_destruction_fall_desolation_jerusalem.html
2 Peter 3:10,11: "But the day of the Lord will come like a thief, and then the heavens will pass away with a mighty roar and the elements will be dissolved by fire and the earth and everything in it will be found out. ... everything is to be dissolved this way," (NAB; "Total destruction is assumed (11)," notes 3,10). "...the heavens will be destroyed by burning, and the elements will melt with intense heat" (2 Peter 3:12). "But by His word the present heavens and earth are being reserved for fire, kept for the day of judgment and destruction of ungodly men" (2 Peter 3:7). Peter's warning reemphasized Zephaniah's warning, where the ancient prophet transmitted the Almighty's words, "I will utterly consume all things from off the face of the ground, saith Jehovah. I will consume man and beast; I will consume the birds of the heavens, and the fishes of the sea, and the stumbling blocks with the wicked; and I will cut off man from off the face of the ground, saith Jehovah" (Zephaniah 1:2,3)
Complete destruction of man on earth is intended. " Their blood will be poured out like dust and their entrails like dung. 18 Neither their silver nor their gold will be able to save them on the day of the LORD’s wrath.” In the fire of his jealousy the whole earth will be consumed, for he will make a sudden end of all who live on the earth (Zephaniah 1:17, 18). The Jehovah's Witnesses theory that they alone, their great crowd, will survive Armageddon and be ruled from heaven by the 144,000 is simply not in accord with Scripture.
Granted, the Jehovah's Witnesses don't believe the earth will be destroyed and base this teaching in large part on Psalm 37:29 where the psalmist wrote, "The just will possess the land (earth) and live in it forever." However, the earth "wears out like a garment (Isa. 51:6), so the word "forever" is hyperbole, and nothing here indicates that there won't be a hiatus, or break, in the earth's habitation. Psalm 37:29 does not say man will inherit the earth continuously without interruption, and Revelation 21:10,27 suggests that reconstituted, glorified man, without the warts, will come back down out of heaven sometime in the future: "He took me in spirit to a great high mountain and showed me the holy city Jerusalem coming down out of heaven from God." "Only those will enter whose names are written in the Lamb's book of life."
Actually, the earth has experienced significant disruptions evidenced by the annihilation of the dinosaurs and great flood of Noah's day. Remember, we are dealing with geologic time, and cycling through another ice age that would wipe off the post-apocalyptic mess left in the wake of Armageddon is entirely within reason; it is more reasonable than handing the Great Crowd brooms and haz-mat suits and ordering them to restore the earth into a paradise.
More to the point is Peter's comparison of the earth's pending fiery destruction to the great flood which is a real, not metaphorical, example of earth's fate as detailed at 2 Peter 3:5-13: "They deliberately ignore the fact that the heavens existed of old and earth was formed out of water and through water by the word of God; through these the world that then existed was destroyed, deluged with water. The present heavens and earth have been reserved by the same word of fire kept for the day of judgment and of destruction of the godless." Jesus likewise made it known that ultimate destruction will be modeled after the destruction of Sodom and Gomorrah, where Luke 17:29 makes it abundantly clear God destroyed them all. That man's governments are changed in the process goes without saying. Remember, "...he was seated on the throne and said, "Behold, I am making all things new. (Rev. 21:5).