The casting out of heaven of Satan and his angels by Archangel Michael per Revelation 12:7-17 is about the end of this world, not back in the old world.
Our Lord Jesus warned us that the last days would be like the days of Noah ("Noe", per Matthew 24:37-39). They were marrying and giving in marriage. Just who was it in Genesis 6 in Noah's day that was doing all the illegitimate marrying and giving in marriage? It was the fallen angels ("sons of God") that looked upon the daughters of Adam, and saw they were fair, and took wives of them, and they begat the giant hybrid race which God later told Israel to destroy in the lands of Canaan.
Just as the enemy has tried to destroy all the skeletal evidence of the giants who once existed on this earth, they also try to destroy what Genesis 6 reveals about Satan's angels taking wives of the daughters of Adam in an attempt to destroy the bloodline that Jesus was to born through.
Even with Noah in Genesis 6, we are told that he was perfect in his bloodline, revealing what the matter was about then.
So if our Lord Jesus warned about the times of Noah for the end, then His servants can be assured that is how it will happen.
Aliens??? Nah, that's the dream from Satan's servants pushed upon the deceived. There is no such thing as extra-terrestrial aliens. They are Satan's angels.
