Then the standard of living for those shrinking generations will continue to fall. It's a damned shame. The thing is, economics are only a part of what is happening. There are health related issues which are probably more important. Low T levels, for a start. Cultural changes too. It's not a good course we're on, so rather than people complaining they're poor, it'd be better for the sake of humanity if they made more babies.
Discussion
Africa is still having lots of kids so humanity will be fine.