Interesting discussion. The simple truth is that we have lots of theories, but real life always messes those up. The one thing we know for sure is that the thin veneer of civilization disappears real fast and people become murderous assholes equally quickly. Interestingly, the become murderous assholes when solitary and murderous assholes when collecting into large groups.
What gun you should have really depends on which part of the country you are in, whether you are staying put in a small community somewhere or heading out. If you plan to be moving, size and weight matter and something as simple as a suppressed 22 (like 10.22 takedown with a suppressor) is not a bad idea. I have enough 22LR ammo squirreled away here and there for multiple generations to be never lacking for ammo.
If you are staying put though and have neighbors you can band together with, what you are looking for is to have some number of decently made ARs that are reliable, lightweight and have simple low power optics. It is a simple truth that most people can't shoot worth a damn and getting someone new to hit a target 50 yards way with a 2x prismatic is much simpler than with irons.
We had that discussion a while back. I think Matt coined the term "Rack Rifle". I joked that is the AK of ARs.
If are seriously concerned about societal collapse, you need simple to operate and maintain rifles in reasonable quantity backed up by serious amounts of ammo.
Now, in principle, it is not a bad idea to have a rifle set-up for a little bit of everything and that is where an LPVO is not a bad idea. Still, emergency situations require redundancy ahead of specialization.
I live in the Southwest, so one thing we have a lot of is the sun. I can maintain some amount of electricity for a good while with a solar panel and a few backup batteries.
The downside is that water is not plentiful here, so aside from lifestraw filters, I'd be looking into somethink like the Source Hydropanel before too long.
ILya