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.