No, that's not what would happen. There are a great many secondary and tertiary systems in place, a breach in one place would not automatically flood the whole country, though of course if you lived in the area just behind the breach it would be a major problem. NL has lived with water long enough that the risks are reasonably well understood. Of course nature can still surprise you, the intensity increase of especially rain has caused some pretty serious problems in recent memory.
But even though we occasionally have a dike that fails something at the level of 1953 isn't going to happen 'just like that', though you can never entirely rule out the possibility.
Much more money has gone into water management since then, it is our 'Los Alamos', special water management taxes have been used for massive investments into infrastructure including pumps, dikes, flood barriers and all kinds of less visible work. It isn't perfect, but it is really quite good and I would much rather live here than a few hundred kilometers upstream during a heavy rain season. At least we are no longer in denial that water management is something that you postpone until after the flood.
Does the Netherlands export their knowledge of handling below sea level engineering? With coasts around the world more prone to flooding it seems like it could be a lucrative industry
One interesting bit about the Kansai Airport work was that the Dutch advised the Japanese to leave the reclaimed land untouched for a while (20 years or so) so it could settle, the Japanese ignored the advice because they had run the numbers and realized dealing with the damage from the settling was more profitable.
We're cheap, it's a local joke that copper wire was invented by two Dutch traders fighting over a single coin, I think the idea of wasting good materials on unstable ground just didn't sit right with the Dutch engineers but the Japanese had no problem with it at all. I wonder how the Japanese look at this today from a financial perspective.
At least Florida can be abandoned in a worst case scenario and the US would continue to function.