Interesting thoughts... As far as I gather (please note I'm only 80 pages into the first Sin War book and 20 pages into Legacy of Blood so I may not be the best source) the only angel with a strong desire to see humans succeed is Tyreal who was quite helpful in D2. The other angels don't really care what happens to Sanctuary as long as the forces of Hell don't use the humans against Heaven. Since Diablo 2 was mostly humans fighting demons rather than joining up with them, I don't see a real reason for the angels to try and intervene. Although, perhaps it would've been a good time... since there were humans fighting the forces of Hell it wouldn't have hurt the angels to side up with them, even if only momentarily.
I believe Tyrael explicitly states in one of his speeches that he has been "forbidden" to aid your player character. "...for this is the hour of mortal man's triumph...your triumph."
I have a sneaking suspicion that there will be some kind of celestial battle on Sanctuary in D3, because the teaser makes a reference to "the end of all things" and that sounds a lot like Armageddon to me.
Is this part of the angels plans for the Humans' redemption? sacrifice?
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the real Heaven is the heavens - absolution.
Thus the angels that fight do so for others, unto themselves - and fuel the fires of hell.
Now that the Great Conflict has come to Sanctuary - will there be angels in flight?
Will the angels wish to let Sanctuary purge in holy fire? Or will they help to protect it, as that which angels do - unto themselves.
I have a sneaking suspicion that there will be some kind of celestial battle on Sanctuary in D3, because the teaser makes a reference to "the end of all things" and that sounds a lot like Armageddon to me.