Not necessarily from this particular set of people though.
Reich: In Europe where we have the best data currently—although that will change over the coming years—we know a lot about how people have migrated. We know of multiple layers of population replacement over the last 50,000 years.
There are about 200 generations between now and then. Your ancestor set needs to only grow by about 10% each generation to include everyone who was alive back then and therefore also them. In a perfectly mixed population your ancestor set grows 100% each generation until it includes everyone. Now humans aren't a perfectly mixed population but you only need a few migrants each century between different societies to reach 10% because in each society it's much closer to 100% (until it includes ~everyone in that society).
Yes, everyone in a region is likely related to ancestors +800 years ago from that region, it's not the same for regions with little migratory exchange.
Probably every Chinese person is a descendant of the 1st Han Emperor, but probably most Europeans are not, though they are probably all descendants of Charlemagne, whereas Chinese citizens are not. Etc.
No. It's very unlikely that the vast majority of people in Africa, Asia, and America are descended from these people. They do almost certainly share a common ancestor, though.
Reich: In Europe where we have the best data currently—although that will change over the coming years—we know a lot about how people have migrated. We know of multiple layers of population replacement over the last 50,000 years.
https://www.theatlantic.com/science/archive/2018/03/ancient-...