The civilians will trap themselves in pits. They will work to starvation. They will get stuck in suicide chains where one dies to a monster, so another feels compelled to go gather their bones, and then they die, and so on. Of course, this is a feature, not a bug: The challenge in games of this genre is to learn the citizens' default behaviors and modify it. You set the highest priorities to gathering and producing food. You tell them that you don't want any more bones, and you give them weapons and armor so they stop dying quite so much. You tweak zones, production schedules, and task priorities to keep everyone happy and healthy.
For example, a standard start-up sequence in Towns goes like this: Do some logging, create a zone for carpentry, build a carpenters' table and a wood detailer. Then mine some stone, and make a masonry area, and then make a mason's bench. Then till some fields, gather some wheat, and plant it. Then make a bakery, equipped with a mill, an oven, and a bakers table. Then you take wheat to the mill, which produces flour, which you then bake into bread, which your civilians can now eat.
