The key part about this is that this is going to shrink the supply of labour faster then the demand. All the old factories and so forth will still be around. So this strengthens the position of workers against the capital. We also will keep a lot of the old infrastructure. In Western Europe, where we have long term financial data going back centuries, there have been two periods of the wealth gap closing. One was after the Black Death and the other after WW2. In both cases there was a lot of death shrinking the labour force.
The other key part is that this is already happening. There was a peak in births in 1990 with 143.5million globally. After that it fell for a bit to then hit another peak in 2012 with 146.1million. Current UN projects are that that will be the peak in the foreseeable future.
This is why the leadership class is talking about birth rates so much. They are worried about their power.
The ones organizing the best. You can see that with unions, politics and a lot of other things. Falling number of people of working age can be dealt with somewhat by forcing people to work. Any way to fight it or even reduce working time per person, by a shorter work week, earlier retirement or even work day helps. Obviously it also depends on industry and global competition. However it currently looks like the system of globalization is splitting up a bit.