So, binging the whole thing twice in a few days ...
Zworgue saw that the angels were murdering tail-born children; the bird-angel war was started because the birds wanted to save one of them. The angels, as well as the others from the beginning, took the old legends of "A child born with a tail shall be the end of our world" as a bad thing, rather than a good/next thing.
On seeing what the angels were doing, he went along with the plan from the pool. Unfortunately, he was spotted (darn those self fulfilling prophecies ... To save your world from the ancients, you must do this. Of course, you won't succeed, and it's your effort that triggers what the ancients were trying to accomplish), and jailed. We see Forma helping the birds give birth, and we see Zworgue in jail -- but we never see what happened to turn them from deep friendship into bitter foes.
And, I cannot believe how many times I read this, and only caught it on the last read-through. The dragon lost a bet, and had to chance its family name to Deception. This is where our Dragon got his family name.
Another loose end: Jason's eye lenses fall through a crack before he can be reactivated.
I don't think we'll ever see the rest of the story at this point. Looks like this hiatus has claimed them the way Agatha wanted Deccy to go.