The intermingled, surviving members of the two races eventually started life on the surface of the planet Earth.
There were some who stayed inside the hollow moon with the royalty from both planets. (Some of the Mayan elite who later came to the planet, were their progeny.) Even here — inside and on the moon's surface — the Builder Race had previously left structures. (This is something the human astronauts discovered when they went to the moon.) On Earth some of their structures have yet to be discovered.
The ruling elite had the ability to watch their subjects' development with the moon's equipment. Till today they have been the shadow elite that has dictated life on Earth in many ways.
The parts of the population that had stayed around the royalty inside the moon, had multiplied into tens of thousands when another catastrophe wiped most of them out. (The inside caverns of the moon were as large as a big city on Earth.)
To be continued...