I suppose Frontier living doesn't necessitate hunting, but the amount of readily available meat and animal products would have to drop very low.

I think the problem really becomes - what do you do when the current system becomes untenable? If the costs of a "basic" modern life (housing, transport, food - I'm not even including healthcare here) become impossible for someone on the median income to have, then what, exactly, are they supposed to do? Find a nice corner to die in?

We sorta tried a miniature version of this on a few acres in Ireland and while it was tough (and we were always reliant on the outside world, we didn't literally homestead), I'm not sure it wouldn't be an improvement for a non-trivial percentage of people at the bottom levels of society.

But, of course, land is owned (thanks to enclosure, which took a common asset and allocated it to specific individuals), and this all falls apart when you or a loved one have a serious disability or illness.

Next is amount of people. Current human density is supported by antibiotics. Take away them and we quickly fall back to around 1900 population density (1.6 billion roughly). And not even internal antibiotics, external antibiotics like chlorine for cleaning and water purification.

So those are the setups for population collapse. When population starts collapsing this way it generally overshoots the numbers pruned because of war/disease. We won't fall to 1.6 billion, it's likely to fall well below 1 billion.