I beat the boss I was working on, without needing to embrace a civilian!
In the setting of the fight, there is an unconscious priest. When the boss reaches 66% for the first time, she will drain the priest, healing back up and boosting her power. In theory, you can drain the priest first, and prevent the boss from healing and powering up.
I decided that--since the priest was going to die anyways--I would try draining him first, and see if that made the fight easier.
I started the fight, but could not figure out how to actually drain the priest. I'm not sure If I was standing in the wrong spot, or pressing the wrong button, or if you need to wait for a specific moment. But since the boss was constantly pressing the attack, I didn't have a lot of time to experiment.
Eventually the boss hit the 66% mark, and drained the priest. So I figured I may as well play out the fight and try again. Only I actually defeated the boss in that attempt!
There was one dicey moment in the last phase when I got really low on health, but I was able to dodge away and heal up.
Now I'm on to Act II, and the citizens remain alive. We'll see if that state of affairs continues. All the enemies in the new area are around level 28 compared to my level 21, so I have to be pretty careful.