They got everybody out. Cavemen, Conquistadors, Cowboys, and whoever else.
If not, whoever's left would live between 100 and 200 years in a cave, regenerating on the Fountain (hence no need for food or water) untin the Sun engulfs the Earth. The ~20,000 AD people seem to value life; they wouldn't just leave them there with no stimuli and slowly going crazy until being incinerated.
