“Heiser’s view is that these intelligences would fall under a different biblical category: the rebellious sons of God—the fallen divine beings or ‘princes of the air’—not demons.”
Those particular angels that rebelled are currently being held in the lower parts of “Hell”, which the bottomless pit which will not be opened until the Day of the Lord. They are not free to roam the earth as the disembodied spirits of the Nephilim are.
Matthew 12:43-45 NKJV
When an unclean spirit goes out of a man, he goes through dry places, seeking rest, and finds none. Then he says, ‘I will return to my house from which I came.’ And when he comes, he finds it empty, swept, and put in order. Then he goes and takes with him seven other spirits more wicked than himself, and they enter and dwell there; and the last state of that man is worse than the first. So shall it also be with this wicked generation.
Luke 8:30-31 NKJV
Jesus asked him, saying, “What is your name?”
And he said, “Legion,” because many demons had entered him. And they begged Him that He would not command them to go out into the abyss.
2 Peter 2:4 NKJV
God did not spare the angels who sinned, but cast them down to hell and delivered them into chains of darkness, to be reserved for judgment.
Revelation 9:1-3 NKJV
Then the fifth angel sounded: And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit. And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit. Then out of the smoke locusts came upon the earth. And to them was given power, as the scorpions of the earth have power.