The Hispanic birthrate in the US is twice the birthrate of the general population. And 45% are born out of wedlock.
This is more a return to the tribalistic society: one filled with internecine war and blood feuds.
This is what we rose up from when we became "domesticated".
So maybe the fecund will survive, but instead of a few small communities of the faithful, there will be urban battle zones filled with warring tribes.