I think it would be more likely for the Overlords to stop existing than to reform.
It could be that some of the Overlords are good now, but evil ones seem more common or at least more influential. The overlords never really agree with each other on anything though, so the religious leaders are mostly evil men who pick among the many voices for those that seem darkest, most powerful, and most willing to share that power.
Although Kael wants to keep the exact details a secret, we know that Danalin is dreaming of Hemah, and it seems likely that it is Hemah who created the Overlords. I tend to think that Hamah is Danalin's "avatar" in creation, and would likely have all the power of a god if he only realized it. Danalin would have spent so much time in his dream that he may consider Hemah his real self now and continue to have such a personality once he awakens. Hemah is not an evil man, but he isn't as gentile as the old Danalin. He seems quite able to experience the whole range of human emotions rather than just manifesting his precept, but tying into his power fully might change that back. It is not in the nature of water to initiate change though (it just goes with the flow rather than initiating or resisting), so even if he does figure things out he may prefer to stick with a mortal life rather than guarding his precept. I don't really know what the effects of that might be. It is possible that realizing he is a god would mean he would be in violation of The Compact, and thus allow other gods to invade and start up another godswar.
It seems to me that in the Beltane cycle Hemah's vision of a sleeping god when almost killed by Devon may have started to clue him in to his identity. In real life, falling back to sleep right after starting to wake up is often a way to enter lucid dreaming, which may be what happened here. Hemah may have figured out how to control his dreams, hence his decision that he doesn't need the mask or incense. If so, he is now incredibly powerful, essentially a rouge god unbound by any precept that could make his personality or actions predictable. I don't think really knows who he is though, and may be more concerned avenging old insults against him or winning Thessa's heart than with returning to who he used to be. He may have also come to think of his torments as a normal part of life, and see no reason why life shouldn't be like that for everyone.