This has been in my ongoing day-mares, as if i'd seen it like a memory, for many years now. In those viewings white people do survive, but not many compared to the whole population similar as the western natives nowadays. Further viewings showed that of the entire population only a few thousands survive far into the future, and white people are there.
What is at stake here is the genetic potential for vitality and vigour (important keywords) in our species.
I learned the principles of animal husbandry from experts, and any knowledgeable breeder knows that if you want to keep a breed or species alive you have to pay close attention to genetic diversity that produces vitality and vigour (and in that order too)... or the species quickly decline after a short lived flourish... then the species can't be replaced.
It is very wise to maintain healthy groups of racially pure people, as well as to freely allow mixing of races without prejudice, because this is how a genetically healthy population is sustained over time.
As purebreeds naturally decline, the mixing in of a different breed doesnt destroy a purebreed as people think, it adds vitality and vigour and we know this phenomena well in hybrids. In fact, the creation of genetically diverse breeds involves the mixing of entirely different breeds in a highly strategic manner until specific results are obtained.