Russia will survive the population collapse. Here is why

They are a dictatorship adjacent nation state.

If their population is running out they will just open up immigration from Central Russia and Belarus even further.

The Russian elite are separate from the Russian commoners so the Russian elite are free to do anything it takes to make more money for themselves.

If the population decline slows down the economy they would let in more hoards of foreign immigrants that will make the middle eastern immigrant crisis to Europe look like child's play.

Conclusion:

Russia will become a major immigrant destination in the future similar to Saudi Arabia.