the general idea is nothing was unforeseen it was all a part of the plan even lucifer's' "betrayal" (although lucifer is kind of one of many mistranslation's made throughout christianity's history)
in the religion god created angels as he did everything in creation but only mankind was given free will so only mankind was, is and forever will be able to defy his wishes everything else in creation does as he commands or plans for them to do
so in the case of lucifer's betrayal for example lucifer had no choice he was created to one day betray god and be punished for it then cast out to hell to punish sinners for eternity
nephilim may have a close translation to giant but my reference to them being demons isn't about the meaning of the word nephilim it's about the roll they served after their creation
i also refer to lucifer being a mistranslation because one the guy that did the translation said he translated it wrong he translated a word written in hebrew to english not by literally translating it from hebrew to english but by translating a latin word that was similar to english
gods most loyal angel that judges mortals after death and punishes the wicked on god's behalf is a falling angel named sameal who was never cast out and still resides in the highest kingdoms of heaven
such a waste of time for someone that has no faith in religion to talk about these things as if they are real