Hi Ignatius,
I am sure others will give you more learned feedback, while mine will be just a very brief note based on what I heard and read when I was trying to be a Presbyterian (late 2003-2006). Proponents of Calvinism, when they talk about the Fall, sometimes ask this question: "Does it ever occur to you that nothing ever occurs to God?" By that, they mean that God indeed "predestined" the fall of angels and then the fall of man. Both angels and humans who will have God's favor, and thus will be saved, had been known to God before the beginning of time, before the Creation, and the choice was made by God based solely on His "good pleasure," totally arbitrarily, regardless of any future merits of these angels and humans.
The Orthodox teaching, on the contary (as far as I understand it, and I am not a cleric or theologian), says that God never withholds His grace from anyone, be it an angel or a human. He never "planned" the Fall, He never wanted it and He works constantly to fix the gigantic problems caused by His fallen creation. The Fall happened not because God planned it, but because His intelligent creatures (angels and humans) are agents of free will. Based on absolutely their own volition, they, and not God, decide, whether to obey Him or to rebel against Him, and He does not force the alternative decision (i.e. obey rather than rebel) on anyone, be it angel or human.
There are differences, however, between the fate of fallen humans and that of fallen angels. From what I read in Fathers, esp. St. John of Damascus, I understand that they do not believe that fallen angels can be redeemed. Nevertheless, there exists a theory of the so-called anakatastasis, claiming that eventually, God's entire creation, including even Lucifer himself, will be saved.
Again, that's just a quick note, and I know others will be more helpful.
Best wishes,
George
