Based on my analysis of the Roman Republic/Empire, the country will cease to be anything like it once was at about 10-15% of the original race but it starts to get really bad after 40%. Unfortunately, the time between 40% to 15% takes longer than from 70% to 40% and the country can still function by riding off the success that it once had for hundreds of years.

Those who think a collapse is on its way are mistaken. You will be replaced and life will go on. It will be worse than it was before but rich rulers won't care. And from the perspective of those who replaced you, it'll still be better for them.

However, there's some modern issues such as the welfare state and modern finance. Could prove to be a couple chaotic elements.