I was doing some experimenting wtih stuff and poking around in the code, and saw that the Vaulters main quest has an alternate chapter 5 quest for when a Vaulters custom faction has the Pitiless trait, since it would be impossible to talk to a village for the quest. I made a Valuters faction with Pitiless to see what this alternate quest looks like, but when I finished Chapter 4, the quest for Chapter 5 never showed up.

I was able to trigger the quest manually using the console after enabling modding tools, so the quest is there and functions fine, as rather than talking to a minor village you search a ruin, but it just isn't triggering.