...cannot possibly work.
For one thing, "after the population declines by 50%" you are, nationally speaking, no longer a viable ethnic group in your own country. You are old Germany full of young Turks. Your successors have already moved in and it's their kids who are occupying all those little seats in grades K-3. And their dads and moms are the big-city mayors.
For another thing, "after the population declines by 50%" you are, nationally speaking, no longer fertile.. Look at the average age for females in Germany, Japan, Italy and Austria: 45-50. The average age for females in Palestine (Gaza trip), Yemen, Nigeria and Somalia is 15-20.
Just who did you say would be "more comfortable with starting families"? The perimenopausal fraus of German couldn't do it if they tried.
Destroying a marriage culture is a lot like destroying a farming culture. People have to the mindset, the 10,000 unwritten skills and preferences, and the cultural supports all around them, passed on in a continuous, cross-generational way.
I'm not at all sure that, once destroyed, you can ever get that back again.
Historically, no nations with median ages as high, and fertility rates as low, as Japan and Europe, have ever recovered. It simply has never happened.
Compounding works in populations as well as finance.
An old population is a soon to no longer exist population.