One thing that struck her as odd when she glanced down into the streets, was that she saw no children, no elderly or infirm members. Even barbarians or monsters should have had children and elders, right?
Ok. The Gnawing Ones have a problem where they are apparently sexless, and require external aid to reproduce. However, the trueborn births in this settlement have been decreasing. This accounts for the lack of children Ling Qi sees.
However! This does not account for the lack of elders. The problem of birth and awakening does not seem to cause the lack of increasing infirmity with age. I'm not inclined to speculate too wildly, since we know only scraps but—
If everyone seems to be in their physical prime, and their "spirit stone mine" can be replenished with tribute of flesh (and maybe spirit)*, do these people kill their infirm members? If they can contribute, are they sacrificed for all the contributions they have left? They seem to return their dead to the river, after all, so its only a short hop to returning the crippled members also.
*(So that's what happened to the flesh and spirit that Thunder Crow Shaman traded! That's a bit of mystery solved! Even more mystery arises, like, what did that spirit fire do? Burning the offered spirit stones, to collect the distilled impurity or discard it?)
There seemed to be a general malaise about, a concern for the 'haul' from the river shrinking, grumbling about lessening rations, complaints about people in 'the city'.
To sum up, this is a spirit stone mine that's dying, meaning the village built around extracting the spirit stones is also dying.
...That comparison to the worst parts of Tonghou is perhaps more apt than Ling Qi may have thought. Tonghou, after all, is a dying city whose spirit stone mines were plundered to uselessness, retaining little importance. The withdrawal of resources to the slums there and the village here is easily paralleled.
[] Infiltrate the fortress by going over the walls (Base DC 40 higher degrees of success allow deeper infiltration, degrees of failure shorten time spent before turning back)
60% chance of success, which is a little too low for my tastes. However, it seems Ling Qi is nigh-guaranteed success at infiltration, with only luck involved in how deep we penetrate.
[] Wait and see if you can spy a group going in or out that you can shadow (Base DC 20, waiting means less time to investigate overall. Failure indicates no opportunity arises)
80% chance of success, which is very high! The problem here is that outright failure means we just fail entirely, and possibly even success involves lesser degrees of success than just flying over.