(Ambiya') 21 : 96
حَتَّىٰ إِذَا فُتِحَتْ يَأْجُوجُ وَمَأْجُوجُ وَهُمْ مِنْ كُلِّ حَدَبٍ يَنْسِلُونَ
Until when Gog and Magog have been let through, and they descend from every hill.
Spreading of Gog and Magog is one among 10 Crucial Signs of Doomsday as explained in verse 6: 158. Until that happens, no people who had been destroyed before will return. See explanation 4: 17-18 and 18: 94.