Deciding whether you should kill the soldiers at Mert's Mill during Blood of Dawnwalker's The Firebrand quest looks like a minor choice at first, but a life does hang on it. After investigating Vlad's house in Laslea, you'll be directed to the mill in the region to the south. When you arrive, though, you'll be confronted by a bunch of soldiers, and you'll have to decide what to do about them.
Should you kill the soldiers or leave them be in Blood of Dawnwalker?
During The Firebrand quest, if you arrive at the farm during the night, you'll be ambushed by some soldiers who demand your identity. You can talk your way out of it by saying "I'm Mirto", but if you kill them Mert's wife Renna will emerge and tell you that you've made a grave mistake and that she'll be punished as a rebel collaborator, considering Mert is already in prison at Stoneward Post.
If you come during the day instead, Renna will pretend you've come to fix the cart. She will explain what's going on and ask you not to kill the soldiers hiding in the barn, again, to avoid making her appear to be a rebel. She's totally wrong, though. You should absolutely kill the soldiers in the barn because otherwise Renna will be killed while you're off trying to free Mert from prison. If you didn't kill the soldiers, Renna's corpse will be lying in the middle of the farm when you get back from your rescue.
I haven't tested whether there are consequences for putting off this quest for too long, so I'd suggest getting Mert out as soon as possible. After jailbreaking Mert, you tell him to flee with Renna to the Svartrau Almshouse and leave the area. If you killed the soldiers, you won't find Renna's corpse when you return to the farm, meaning they presumably got out safely.
You can meet Mert again at the Almshouse in Svartrau Cathedral's complex later, so be sure to check in on him when passing through.
