The article you linked doesn't talk about the "decline" being related to aging populace with a low birth rate.

But like, they sent back a bazillion Japanese Brazilians a little while ago because they were immigrants. Full blooded Japanese, but immigrants, so deport with ye! I think maybe in order to continue healthily they will have to stop deporting immigrants, and other such things along that line. They may have to sacrifice tending towards mono-ethnic to save everyone.

Banding together in a catastrophe is a good thing...but not really related to the source of any kind of decline.

This is of course, from what I know. It is possible that I have flawed info.