Many people say gradually, and that there is 'a lot of ruin in a nation' - they believe in 'graceful' degradation.
But complex (interconnected) systems are different - they are more efficient than simple systems, and better at tolerating modest deviations from normal; however, highly complex systems degrade suddenly, and catastrophically, due to their multiple inter-dependencies.
Previous human societies were 'segmentary' - composed of mostly-autonomous, (and mostly self-directed) units. Each can subsist after a catastrophe, and replicate to make like themselves.
But we are living in the least segmetary society ever.
In the UK, almost every vestige of segmentary organization (local government, the professions and trades, universities, societies and clubs) have been destroyed, or subverted and absorbed into the national government; and the national government has experienced the same with respect to the European Union.
Power and responsibility are dissociated. Spontaneous self-organization - gone. Autonomy - gone. Self-help - gone, crushed, illegal; to be replaced by dependence; demands for 'rights', subsidies, looking-after.
So I think sudden, catastrophic collapse is the likelihood - and the degree of collapse and disorder would then be much greater than in the past (since there is little or nothing to stop this) - and the recovery will be much slower/ more difficult than in the past.
Have a Nice Day!