There are many people who live in Vally. How this culture of one building survived the pounding of time to become a country is beyond me. I suppose that if there were an uprising of the clans against the power of the Man and Stance Mans this country would just fall apart. But as the people of the clans hold those in charge to be some kind of gods I don't think this will happen. Periodically there are individuals of the clans, and of the groups also, who decide not to live in Vally anymore and they do leave. But there is no general uprising of the people to leave Vally.
I have some confusion as why the Man and the Stance Mans allow the religion of the Sea Sems to flourish. But my only guess it is the odd power of the Sumers over the Man and Stance Mans. For though they seem to prefer the clans to worship them, the stopping of the Sea Sems religion just might kill the tourist business in Vally.
As for the missing people I can only assume as the culture moved from the single building to being a country their functionality was lost. But as I stated before I don't think they people who performed these duties were lost. I believe they were simply absorbed into other groups of people.