KP, as others have said, welcome to Epic.
The amount of edge left on a ski is not like the amount of rubber tread left on a tire. As the tire wears out, it will gradually perform more poorly (on wet/snowy roads). When its finally totally bald, you will be skidding all over the place on wet roads.
Skis are not like this. As a ski's edge gets thinner (from successive tunings), you will probably not notice any change whatsoever in its performance until it becomes so thin that it finally breaks either (a) while in use (from the most minor of trauma), or (b) when tuning.
So, if you are asking how many ski days can you get out of a pair of skis with half their edge gone, but using good conservative tuning technique, the answer is probably in excess of 50 days if you never hit anything. However, the thinner the edges are, the less trauma it will take for something to irreparably damage them. Estimating when this will happen is like estimating how long it will be until you run over the next nail in the road, hit a really deep pothole, etc. Another analogy might be estimating how long someone will live who is currently 50 years old and in good health. The variability is huge - they might make it to age 100, or they might stay perfectly healthy until they get hit by a car or come down with some uncontrolable infection in the next six months.
From your location, I presume you sometimes ski in southern Poland. Friends who have skied there tell me that their snowmaking and grooming is much worse than in the USA, so you won't have to be doing anything extreme like "racing over rocks" to eventually have a close encounter of the kind you won't like. Its inevitable here, and its probably even more likely over there.
About the best you can do is take reasonable care and just run them till they die.
Tom / PM
PS - Why don't you tell us something about yourself and what skiing is like in your part of the world? I'm sure most people on Epic would love to know more about it. Is southern Poland indeed your "home" ski area? Do you have any pictures you could post? I see someone mentioned racing in Lithuania. Is this a big thing in Latvia as well? I hear that since Putin skis, skiing in Russia has become extremely popular. Has any of this carried over to Latvia, or maybe the dislike of anything related to the former USSR has had the opposite effect?