Ok, name one authoritarian state that never fell, besides the authoritarian states we have today?

Of course it eventually falls down, everything does. I'm not saying it won't be difficult, nor many people will ultimately die, and the country will be very different. But it will happen, if not sooner, then later, like in every other place in the world.

> Ok, name one authoritarian state that never fell, besides the authoritarian states we have today?

By defintion, if it “never fell”, it would be one of the authoritarian states we have today, so the obvious lack of any example fulfilling that criteria doesn't demonstrate anything one way or the other.

Now, if you could say something like “point to any authoritarian regime existing after <year> that had existed for longer than <span in years>”, that might tend to support the claim that, at least after a certain point in time, authoritarian regimes tended to have a particular finite lifespan (of course, you can never prove that currently-existing regimes aren’t exceptions to that withot access to future knowledge.)

At one point I had a hypothesis based on a few notable examples that with certain definitional bounds this might work with some point in the 20th century and about 80 years (even had a bit of process explanation, though not a strong theory on why it didn't apply earlier beyond the general spread of democratic ideals) but I never rigourously checked if there might be exceptions.

(Of course, plenty of authoritarian regimes fall only to be replaced by different authoritarian regimes, too.)