The countries at the bottom of this list seem much more pleasant to live in than the countries at the top: http://en.wikipedia.org/wiki/List_of_sovereign_states_and_de...
If you don't replace yourself, you're a dead end, a historical curiosity at some point if you're lucky. Imagine a Japan that is one day remember mostly for and about it's anime and manga.... And, oh, yeah, they found a superior way to make good quality cars, assuming we're still using those in the 24th and a Half Century.
They need to slow population decline but a decline is good for that country for a little while. Way too many people, too long of lines. They need more leisure time and less stress there.
That's simply not an option for a country with as big a welfare state as Japan's, unless of course they take the Soylent Green approach, which would seem to be at odds with the cultural respect for the elderly, ancestors, etc. (maybe that's changing). Add the government essentially misappropriating the people's wealth to fund decades of extreme fiscal deficits, to the point of 214% of GDP per the CIA and 238% per the IMF (per Wikipedia https://en.wikipedia.org/wiki/List_of_countries_by_public_de...) ... as more and more people retire, the money they thought they had in their e.g. Japan Post Bank, they're not going to be able to withdraw it, at least in vaguely similar economic terms.
I don't know what the hell they can do, that doesn't involve serious inhuman stuff.
This is one of the reasons they are investing heavily into robotics. That is the inhuman that might save them.
Their economic system is so broken I'm not sure more robotics would make a qualitative difference in the outcome.
Besides the immediate problems (including the prefectures dropping on the floor the information necessary for old age pension payments for way too many who didn't work for big companies, those in the high risk/low reward part of the economy), e.g. see https://en.wikipedia.org/wiki/Aging_of_Japan, there will be no Japanese people by the end of the next century, and given the tough neighborhood they live in, "the end" will probably come much sooner.