It will shatter, it will break, it will crush...
Over time, and depending what youre doing with it, I suppose you can destroy anything. Still, my experience over time has been, the kydex hold up much better, and are usually half the price of a decent leather holster to boot.
The holster on the right is the original Blade Tech holster I was referring to above. The holster on the left, was a new one I bought as a back up, which was never used. As you can see, a small portion of the sweat guard at the top of the original holster did in fact break off, and I dont remember now, how it happened. Other than that, and replacing a couple of straps over the 10 or so years I used it, nothing else was an issue.
This is a close up of the gun in the above pic, a Colt Combat Commander. It started life as a blued gun, and lasted about a year in leather holsters before the rust got bad enough it needed attention. I had it hard chromed just prior to getting the Blade Tech. What appears to be "black" streaks on the gun are in fact, polished chrome, where the gun contacted the holster. Those marks are 10 years worth of wear and hard use. The gun was usually shot three or four times a month and drawn from its holster on a pretty much daily basis in practice. As you can see, other than those marks, the rest of the finish is in pretty good shape, with just a small amount of "powder" rust where the grip was exposed to my body.
This is a pic of the last Royal Guard I had, and was in use just before and after the hard chrome job. The holster had about a months worth of use on it when the pic was taken, and the duct tape was a feeble attempt at stopping the sweat from soaking through. It didnt work. When that pic was taken, the holster had been sitting in an old "holster" box for a number of years, and actually doesnt look to bad.
I wonder if the tupperware pistols will still be carried in tupperware holsters 100 years from now or if they will be like last night's casserole, just leftovers in a tupperware box.
Actually, "Tupperware" is really the best thing to carry in a leather IWB holster, as its not affected by what it has to live and deal with. The carrier on the other hand, is the one who may well do the suffering.
Its not that I'm against leather holsters, its just certain types and for certain uses. I too like a nice, well made OWB holster on a nice leather belt, carrying a deeply blued, and nicely wood stocked handgun out to a BBQ. I would never wear any of them to work or where I play though.
Like I said earlier, you may have a total different experience with them, if youre lifestyle is different than mine. If you carry IWB, are active, and work/live/play outside, year round, especially if the heat and humidity is anything like it is here in the summer, then you may want to consider looking into kydex, and this is especially so if you sweat a lot.
I dont care what you treat leather with, it will eventually stop working, just like the old leather boot treatments (been there, done that, suffered for years, and now wont buy anything that doenst have a goretex bootie!) and will begin to take on moisture. Then theres also the issue of what those treatments will do for your skin if its irritated.
Hey, the only real way to find out what works best for you, is to try them all and see how it goes. You dont need the holster box anymore, as EBay is a great place to sell the old ones, and try out new ones at a better price. Dont get to caught up on what the holster does to your gun either, if you wear it all the time, its going to get beat up. Thats just the way it is.