The descent of the serpents may have wiped out a vast number of lives, but due to the fact that the essence of those lost lives was not consumed by them and the Great Desert was destabilized, it meant a significant number of these immortals could be resurrected.
Those who could not return were either too weak or had perished entirely; the feedback from the power of destruction had proved too much for their dimensional powers to handle.
And so billions of immortals began to slowly rise out of ashes, but they were smart about their resurrection and chose to return far away from the desert.
By coincidental stroke of fate, the immortals who died turned out to be the lucky ones. Death shielded them from the full collapse of sanity caused by the descent of the serpents. For those that survived, only a few were able to keep their minds intact, and all were Old Ones.
