"thus it is impossible to predict when, or whether, it [the shrinkage of Russia's population] will finally come to an end"
That's some loopy hyperbole, right there. Babies are still being born in Russia. Even a shockingly huge drop in population due to low replacement will eventually end in a stable population size.
I don't understand your math. If the birth rate stays lower than replacement, and the average life span does not increase, at what point would the population stabilize?
At the point in which the number of births constitutes replacement. We're not talking 5 babies born annually in the Rodina, we're talking a small number of babies born compared to Russia's population.
Births aren't evenly-distributed. The population segments that are having more births now are the segments likely to have more births down the road. Death, on the other hand, is much more evenly distributed, and the number of deaths per year is directly related to population. As the population shrinks, you have a smaller number of deaths, but births don't decrease as quickly. Eventually, you hit a new equilibrium.
That's some loopy hyperbole, right there. Babies are still being born in Russia. Even a shockingly huge drop in population due to low replacement will eventually end in a stable population size.