What are the steps to overcome a state in which miners couldn't mine blocks? The difficulty is set according to the total hash rate of the network.

Is there a possibility in which miners just can't validate blocks (will not find hash that will satisfy the POW)?

I understand the probability.

there's a very small percent where they couldn't do it, is that assumption wrong?

If a situation like that is possible, what will be the solution?

As far as I understand, there will be an adjustment of the POW, decrease the difficulty, until somebody will find block?

I'm trying to understand if a potential risk to the blockchain exists at that point.
A hash that can satisfy the PoW can always be found, the only determinant is time. This is identical to coin flipping - you can always flip a head, you just have to keep flipping until you do.

On average it takes ten minutes to find a hash, but let's consider something very dramatic has happened: let's say the Chinese have cut all links to the outside world, the Americans have successfully banned all Bitcoin activity, and the Europeans have a topsekrit piece of code that successfully intercepts and scrambles anything uploaded from one of their miners. Let's say that all of that happened inside the time it takes to mine one block, and let's say that for whatever reason there is now one single, solitary, functional miner anywhere on the planet, it's a Raspberry Pi, and it'll take Eleventy years to mine the next block. And a hundredteen times longer to reach the next difficulty adjustment. I think you'll agree that this is a state in which miners couldn't mine blocks. What then?

The most obvious step is a hard fork that resets the difficulty for that one miner. The miner will obviously agree; those using the blockchain would rather have that fork than wait in hope too.