I didn't read them all, but I have read enough to know I have to reply.
Going straight to the OPs post.
The case is unsuitable to load when the primer goes in too easily. What is too easy? Jack O'Connor once wrote that when you could push the primer in with your thumb, it went in too easy. With all due respect to O'Connor, I think that is much too easy. I go by the feel of the power it takes to seat the primer. If it is about half of what it usually takes, I throw away the case.
What is the worst catastoghic happening of using a case too often?
Nothing catastrophic, but something you don't want to happen is for the primer to blow out. Big noise, fireball around the action, maybe extractor blown off.
Someone said if the primer pockets are increasing in size, you may be loading a bit hot!
The understatement of the day. If the primer loosens with only one or two shots, you are dangerously over loading. They tell us that proof loads won't loosen the primer with only a shot or two.
We are often told on here that loading heavy shortens case life. I think this is only true if the loads are so heavy that the primers loosen. For the vast majority of rifles, the listed maximum loads in reloading manuals, will never loosen primers and my opinion is these loads will not shorten case life any more than would cases loaded to only the starting loads in the books.
I am not known as one who loads light. I load to what my rifle will handle safely and this is often heavier than shown in loading books. Still, I get very long life from my cases and unless something unusual happens, my primers never loosen. I still have old CIL and Norma cases around, which in the past have been loaded countless times. I recently worked on them and every single one I tried had a tight primer pocket. Looking at the case they looked like once shot cases!
While head seperation, just above the web, sounds pretty dire, the shooter never knows it happens until the bolt is opened and only a short piece of case comes out! I have shot on the range where the fellow next to me with a 30-06 had almost every case come out, barely holding together at this spot. Some cases would be open three quarters of the way around them, but nothing, whatsoever, was noticed in shooting them. Finally, one broke off completely and he had to quit shooting because he didn't have a broken case extractor with him.
Target shooters often carried a broken case extractor with them at shooting matches. Hunters often had one with them on long hunting trips, also.
So, how does a case wear out and become unuseable?
They get lengthwise cracks in the necks. This is the normal way for a case to end its useful life span. This presents no danger to the shooter. For non important loading, I have often loaded a case with a slight crack, or line, which I know will open up on shooting the next round.