The rate is 0.72. Every 20 years you lose 20% of your population or a percent a year. That would give South Korea 100 years of existence at this point. It’s dire.
Pretty sure your maths is off - even if it did steadily fall by 20% every 20 years, it'd still have a population of 16 to 17 million in 100 years' time. So no, not especially dire.