They are not dying out, This "White people are dying out" is a conspiracy theory called the Great Replacement a.k.a the White Genocide before they re-branded it, It was created by these right-wing sh!iheads to find a justification to kill millions of people. This video below made a good job debunking it, He took data from one of these Neo-Nazi sh!iheads, Extrapolated the data and showed even if the Migrants don't integrate into those societies it takes 450 years for the migrants to outbreed the Whites in those countries.
So, there's no replacement going on, This is a lie literally created by the same Neo-Nazi sh!iheads who want to kill millions of people because of it, Don't spread their lies.