2Pe 2:4 (ASV) For if God spared not angels when they sinned, but cast them down to hell, and committed them to pits of darkness, to be reserved unto judgment;
God sent sinful angels to Hell as their judgment. They are not there “waiting for their own judgment.
Mt 25:41 Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:
They were judged/evaluated and sent to Hell, and mankind’s exposure to those eternal beings is punishment for opposing God.
God uses them for the judgment of others as Isaiah 26:11 shows.
Isa 26:11 LORD, when thy hand is lifted up, they will not see: but they shall see, and be ashamed for their envy at the people; yea, the fire of thine enemies shall devour them.
God’s enemies embody the fire.
Angels are not subject to death as Heb 2:9 illustrates.
Heb 2:9 But we see Jesus, who was made a little lower than the angels for the suffering of death, crowned with glory and honour; that he by the grace of God should taste death for every man.
They dwell in everlasting fire or Hell.
Isaiah 26:11 shows that the fire that the fallen angels dwell in is employed by God to consume His enemies.
The Devil and His angels consume dust, which is what Mankind was formed from.
Ge 2:7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
Ge 3:14 ¶ And the LORD God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life:
In summary – We see Fallen angels or Hellfire being used to discipline those who oppose God. This does not always result in destruction. Sometimes the result is purification as is shown in the following verses.
1Co 11:32 But when we are judged, we are chastened of the Lord, that we should not be condemned with the world.
Isa 48:10 (RSV) Behold, I have refined you, but not like silver; I have tried you in the furnace of affliction.
Mt 3:12 Whose fan is in his hand, and he will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire.