Hi TD
I think that The Bible principle concerning those that have perfection, is that it will last until they willfully do something that makes them imperfect.
So once the Angels came down to earth doing what was clearly forbidden to them, willfully they became imperfect and hense why their children (obviously imperfect because they could die) all died at the flood. These angels were then kept bound until judgement.
Jude 1:6 (New International Version)
6 And the angels who did not keep their positions of authority but abandoned their own home—these he has kept in darkness, bound with everlasting chains for judgment on the great Day.