So, how much it is possible, that the wings disconnect from a plane due to turbulence?
0.000000000000001 percent. The wing is like one piece. It will never disconnect by itself. Unless the plane collide with other plane while airborne.
Can a plain land successfully without one wing?
Technically, it is one wing (because it is one piece), therefore the plane will not land without that wing! Again, the wing can not be disconnected by itself
Will the drop in the plane's speed or increase in the attack angle lead to the engine surging ("pompage") that leads to stopping of the engine?
No, the engines will not stop easily! you are flying a 747, not a Cessna. BTW, 747 has 4 engines and it can land with two only. In worst cases were engines stop, the pilots will have time to restart the engines. They need like 30 seconds to do so and they most likely will be on 30,000-40,000 feet so they got all the time in the world.
Does the pompage have positive feedback (i.e. pompage in one engine leads to further decrease in speed so that other engines experience it)?
No, if one engine is gone (or two in 747) other engines will continue to work. Pilots will increase the power in the remaining engine(s) and passengers will not even notice.
Is it true that the most modern airliners cannot land without engines working?
All airplanes can glide with no engines, if they have some altitude and they find a good landing spot like a field or a lake then the plane can land, check TACA airlines accident and Hudson river accident.
Does the drop of the speed and rising angle of attack inevitably lead the plane to a flat spin?
That's how aerodynamics are, but why would a pilot do that? any way most airplanes have an auto correction ability, so even if the pilot did not try to fix it, the plane will correct the spin!
It it true that civil pilots are not trained to get a plane back from a flat spin?
This is totally wrong. All pilots are trained for that.
Is it true that civil airliners usually not equipped with anti-spin parachutes so that getting out of lat spin is impossible after first turn?
No parachutes, my friend. No real life aircraft have them!
I am a cabin crew member for years, I had all kind of weird airplanes stuff and I never had 1% of these thoughts you had. I had flights with 747 where pilots had to switch off 1 engine (engine flame out) and I landed safely, I had flights with 1 engine in twin engine aircraft (also landed safely as you can see) and I can tell you this: flying in airplanes is much much much safer than driving a car.
If these questions are out of curiosity then you got the answers, if these questions are out of real fear and thoughts you have in your head then I strongly suggest talking to some professional to get some help in clearing these fears from your head.