Just a quick thought. The crazy thing about sotah is that it works about equally well if it kills nobody at all. Think about it- it is only used when there are only two people who know whether or not the woman is guilty, and both of them have a vested interest in keeping the information secret. If the woman is actually guilty and nonetheless gets away with it, she's hardly going to tell anyone. She goes off, perhaps with her faith challenged, perhaps thinking at her husband cheated on her, but the husband is happy and the society continues to function thinking that everything works.
The more important use of the water is to keep everybody scared off, both of adultery and later of failing to admit it and agreeing to go through the ritual. Even if nobody ever dies, belief in the efficacy of the whole thing is probably not going to be shaken- firstly, because there's a general presumption that only the innocent would dare to go through with something that they know will kill the guilty and is besides shameful and scary, and secondly, because the whole thing is probably so rare that nobody thinks that there's an overwhelming trend (after all, they stopped the practice when there were a lot of adulterers.) And when everyone really does believe in it, only the innocent will dare to go through with it, so that there becomes absolutely no practical impact to the question of whether it would kill the guilty.
Everyone avoids adultery to a large degree, chooses uncompensated divorce the rest of the time, and the truly innocent have a foolproof way of convincing their communities and husbands of their innocence, all without actually ever requiring open miracles. Not that I'm saying that it didn't actually work the way the text claims- miracles and all- but it doesn't need to. (And after all, the gemara says that even G-d lies for shalom bayit....)