I don't disagree! Maybe you were talking to a super-prepper.
However to play Devil's Advocate I expect you could survive Argentina/Rwanda/Georgia/Ukraine with sufficient preparation e.g. growing food underground.
It just takes an ungodly amount of money to make it work.
> I'd challenge anyone to show when such a thing has happened in history.
That's the interesting problem because I'd say (let's call it) 'cannibal holocaust' does happen with some frequency on a historical scale. It happened in my country and Russia more recently. It's rare but it does happen.
The key element I think isn't so much resources as secrecy of preparations. With sufficient resources and thought you should be able to hole up for the rest of your life.
Whether you'd want to is another issue!
You have to remember that the people who do go fully off the grid aren't all that likely to advertise themselves. I'm thinking they will mostly be dissidents or the military (for deadman's switches, secret bioweapon programs and the like). So your appeal for challengers might come up empty for reasons other than non-existence. People who do this are always going to be pretty extreme.
Here's one example: http://www.smithsonianmag.com/history/for-40-years-this-russ...
I wouldn't say they were prepared with bullets and MREs per se but they certainly got off the grid. Also it is an interesting story.
Finally I offer you an example of (intellectual) survival from ancient times in my own country.
The majority of Greek texts you've heard of used to be stored in a small island off the Irish coast, protected against invaders by monks and most likely extreme isolation. If the Carolingian empire hadn't copied them from the monks you'd know next to nothing about the most major figures and events in world history.
https://en.wikipedia.org/wiki/Transmission_of_the_Greek_Clas...
When the Roman empire fell, knowledge of it and its predecessors was really in danger of being lost, despite what modern day hipster hun-apologists will tell you. From literacy to ... not-literacy. Without that backup beyond the furthest corner of the Empire, we'd know nothing about major figures like Seneca and Cicero.
Kenneth Clark did an excellent documentary on the subject if you're interested.
The episode is: Civilisation (1969) Episode 1 "The Skin of Our Teeth", from 13:35.
I don't know if you're familiar with Neal Stephenson's Anathem but I imagine he got a lot of inspiration from this.