My brothers and sisters in Jesus Christ, the 144,000 on mount Zion (Revelation 7:4-8, 14:1) are there right before the end of the world. When Jesus comes back, he is going to rule for 1,000 years. At the end of that 1,000 years is the end of the world. Those 144,000 are going to be there during:
And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them. Revelation 20:9
That is why scripture says:
And after these things I saw four angels standing on the four corners of the earth, holding the four winds of the earth, that the wind should not blow on the earth, nor on the sea, nor on any tree. And I saw another angel ascending from the east, having the seal of the living God: and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea, Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads. Revelation 7:1-3
- because these scriptures are just about to happen:
And the seventh angel poured out his vial into the air; and there came a great voice out of the temple of heaven, from the throne, saying, It is done. And there were voices, and thunders, and lightnings; and there was a great earthquake, such as was not since men were upon the earth, so mighty an earthquake, and so great. And the great city was divided into three parts, and the cities of the nations fell: and great Babylon came in remembrance before God, to give unto her the cup of the wine of the fierceness of his wrath. And every island fled away, and the mountains were not found. And there fell upon men a great hail out of heaven, every stone about the weight of a talent: and men blasphemed God because of the plague of the hail; for the plague thereof was exceeding great. Revelation 16:17-21
But the word of God says:
(A Song of degrees.) They that trust in the LORD shall be as mount Zion, which cannot be removed, but abideth for ever. Psalms 125:1
So the 144,000 will stay there, as everything happens, as new Jerusalem descends down on them (Revelation 21:2,10), and settles, as they remain there on mount Zion, in new Jerusalem, the firstfruits of God and the Lamb (Revelation 14:4), having passed from this world to the next.
Glory to God.