webdog said:But npetreley, if they did that, they would cease to be referred to as "sons of God". They would be demons.
I think the responses above deal with the issue well (as in being not mortal), but I'll also point out that you're assuming that:
1. You must refer to an angel as a demon in any context where he does something wrong.
2. Demons are fallen angels.
I don't think either assumption is purely scriptural. There's no scriptural rule that if an angel rebels, it must be referred to as a demon.
As for assumption #2, most people assume demons are fallen angels, but the Bible never says that. We don't really know for sure where demons come from. The only thing the Bible says about them that we know for sure is that they are bad, that some demons are more potent than others, and that they seem to be obsessed with possessing flesh in some way or another. While it seems reasonable to assume that demons are fallen angels (since there is a hierarchy among angels as well as demons), the Bible doesn't come right out and say they're fallen angels.
See my other thread for a speculation that demons are the result of dead offspring of angels/women. Is that what demons are? I have no idea, but it's a thought.