The Netherlands is pretty typical for Northern Europe, except for its high density. The demographics of most of Northern Europe are such that most populations have a fertility rate of less than the 2.1 children per woman needed to sustain the same population size. Because of WWII, or rather the babies born after that, most populations in Northern Europe now have a heavy top of old people. Most populations in Northern Europe, and the Netherlands, are still rising because of immigration, where Germany is the sole exception to that. (I think they figured out the anticipated problem.)
So yeah, without immigration the population size would drop, but very slowly. Not fast enough for what I'ld like, anyway.
The US has the opposite 'problem' of Northern Europe, with a lively and young population, btw.