Yes it does and thats why I think its very hard to predict the furture in terms of demographics. History is full of bizarre demographic shifts..and not just tyhe Baby boom after WWII though that is one significant example of how trends can reverse. I grant Steyn that large decreases in population can have profound impacts but they dont necissarily signal the end of a civilization. In the early Eastern Roman empire plague, war and famine had enormous impacts on the demographics of the empire...indeed more than once it looked like it would collapse but the Bizantine empire lasted another thousand years past the fall of Rome.
Demographics don't change overnight. It is like turning around an aircraft carrier. What is happening in Europe is like gradually turning up the heat on a frog in a pot of cold water. By the time they realize what is happening, they will be boiled to death.