Can those angels ever be saved?
Bob Black seems to answer that quite well, with his two verses, one of which I will again share:
Jude 1:6 And the angels who did not keep their proper domain, but left their own abode, He has reserved in everlasting chains under darkness for the judgment of the great day;
To expound on that verse a little, the "proper domain" of the angels is their likeness and proximity with God; "Their own abode" is heaven. Those who did leave their proper domain, God has confined to darkness with everlasting chains. On the day of judgement, the last bonds with God will be broken and they will get what was reserved for them (the "everlasting fire"). I certainly take that to mean that once the demons fell, they have no way of returning. What a great reminder for us to keep on the right path!
Also: Some of the answers to this question seemed to state that angels did not have free will, but were predestined.
Now, I know that some may disagree with what I say here, but I am fully convinced that angels do/did have free will (at this point however, those who have fallen, seem to have no way out).
Note: My reasoning might only be taken seriously by those who believe that men are not predestined, but all have free-will.
According to King David (Ps 8:5):
Thou hast made him a little lower than the angels
So, man is higher than the beasts (who are bound with Obedience to God and can not go against his commands) and lower than the angels... As I see it, The Angels then must have all the things that Man has (don't take me too literally), including free-will.
Forgive me, those of you who think that we are predestined.
Can the angels that remain choose to change sides?
I don't know about anyone else, but I grew up with the knowledge, that, before God's conception in the womb of the virgin, all angels in heaven still had the choice to go against God and follow the Devil. However, once they saw God in the flesh (at the conception), the angels could not fall anymore. That isn't saying that they were restrained, but that they now had no inclination ever to go against their God, now that they saw what He had in store for his creation. I know that this might seem like a Tradition thing, since I can't really think of any verses to go upon, and can't even remember where I first heard this teaching, so I am sorry about having no "proof" for all you Sola Scriptura people out there (also sorry if I seemed to use that term derogatorily; I didn't mean to).
So, my conclusions:
The angels and demons are both stuck where they are at. :)