After the Millennium,
After Satan is cast into the lake of fire,
After the Great White Throne Judgment,
After death and Hades are cast into the lake of fire,
After the second death,
After the new heavens and new earth,
After the New Jerusalem comes down to the earth, we read this:
Revelation 22:14 Blessed are those who do His commandments, that they may have the right to the tree of life, and may enter through the gates into the city. 15 But outside are dogs and sorcerers and sexually immoral and murderers and idolaters, and whoever loves and practices a lie.
Once death and Hades are cast into the lake of fire, it would seem that death no longer exists and thus all living will live forever. First, how then can there be "murderers" outside the New Jerusalem if death is dead? Second, who are these sinners in the age to come?
Revelation 21:23 The city had no need of the sun or of the moon to shine in it, for the glory of God illuminated it. The Lamb is its light. 24 And the nations of those who are saved shall walk in its light, and the kings of the earth bring their glory and honor into it. 25 Its gates shall not be shut at all by day (there shall be no night there). 26 And they shall bring the glory and the honor of the nations into it. 27 But there shall by no means enter it anything that defiles, or causes an abomination or a lie, but only those who are written in the Lamb’s Book of Life.
Perhaps, this description can shed some light, though a bit controversial. Only those written in the Lamb's Book of Life may enter. This suggests that there are some NOT written in the Book but still live on the earth at that time though unable to enter the city. Does this suggest there are two types of "saved" peoples? One group written in the Book and able to enter the city, and another group not written in the Book and unable to enter the city?
If I may complicate the matter even further, at the GWTJ, ANYONE not written in the Book of Life is cast into the lake of fire. (Rev 20:15) It appears that the "Book of Life" is not the same as the "Lamb's Book of Life." Or, not every person is judged that day. Somehow, people not written in the Book still exist after the NHNE.
We understand those written in the Lamb's Book of Life, the saved. We also understand the wicked being cast into the lake of fire, hell. But, there is a third group apparently. So, who are these sinners that live forever?