ANSWER: The events to happen after the thousand-year reign of Christ on the earth are described in Revelation 20:5 through to the end of the book of Revelation.
Revelation 20:5 shows that the second resurrection will occur after the millennium: "But the rest of the dead did not live again until the thousand years were finished..." These are not the dead in Christ but simply the dead - those who have not yet had their opportunity for salvation. This will be a resurrection to mortal life (Ezekiel 37:1-14).
During the millennium Satan will be restrained and prevented from deceiving the nations (Revelation 20:1-3). After the thousand years are over Satan will be loosed out of his prison (Revelation 20:7-9) and go out to deceive the humans who are not yet born into God's Kingdom. Satan and the demons will then be cast into the lake of fire (Revelation 20:10). In the lake of fire, they will be powerless to deceive their rest of the dead who will then be resurrected to physical life in the second resurrection (Ezekiel 37:1-14). We read about the second resurrection, also called the Great White Throne Judgement period, in Revelation 20:11-12. This will be a resurrection to mortal life and will include all those who died in ignorance in past ages.
After God's plan of salvation is complete the earth will be cleansed with fire (II Peter 3:10-12). The lake of fire will destroy everything that is physical and will burn itself out after consuming everything combustible on the entire surface of the earth.
Following this "Gehenna fire," God will create a new heaven and a new earth: "And I saw a new heaven and a new earth for the first heaven and the first earth had passed away. Also, there was no more sea. Then I, John, saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. And I heard a loud voice from heaven saying, 'Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people, and God Himself will be with them and be their God" (Revelation 21:1-3). At that time the earth will become the headquarters of the universe for God's Kingdom (Revelation 21, 22).
Hebrews 2:6-8 states that God will ultimately put all things (the entire universe) under the control of Himself and those who will be born into His Family and given immortality (I Corinthians 15:50-54).
Whatever our glorious future will be it will be astonishing beyond imagination (Romans 8:18; II Corinthians 4:17). Those in God's Kingdom will inhabit eternity: "Of the increase of His government and peace there will be no end, upon the throne of David and over His kingdom, to order it and establish it with judgment and justice from that time forward, even forever. The zeal of the LORD of hosts will perform this" (Isaiah 9:7).