I'm not sure how old you are, or whether you've spent enough time in a single such "tribe" to see this in action, but I can tell you this: People come back. They may wander off for five or ten years while they have children who are young enough to need a lot of care. But eventually the kids get old enough, and many of the people who dropped out of sight so they could be parents do return to the tribe.

I prefer to see their disappearances as temporary, and I will patiently wait for them here.