There's no way out of a depopulation spiral other than reversing it or dying out. If they die out some other nation will take over their land, so it's merely a

There's no way out of a depopulation spiral other than reversing it or dying out. If they die out some other nation will take over their land, so it's merely a question of whether the ethnically non-Japanese people who will inhabit the land in the future will call themselves Japanese or not. What happens when a nation has its ethnicity completely replaced? Does it lose its national identity or not?