I’m guessing there aren’t many anarcho-primitivists on the GWC forum 
A common theme is disease, but communicable diseases are much more easily spread in cities than in non-urban societies. I think the main risks would have been trauma and infected wounds. I too am guessing they kept some meds.
As for life expectancy, 20 sounds a little low for the Native Americans prior to colonisation, but I’ll tentatively defer to a reference. Hunter-gatherers typically live into their 30s or 40s, provided they make it into their teens. I know this is still pretty grim but I bet they could extend this with some salvaged medical supplies and some know-how.
On top of that, hunting and gathering is much less like hard work than farming, so maybe people thought farming was just a dumb idea. There are plenty of studies that indicate the “working week” for hunters and gatherers is way lower than that of farmers. And hunter-gatherer groups, like most “uncivilised” societies are generally much more equal, and afford greater individual autonomy within the context of group cooperation. If they wanted to build agricultural societies with technology and government they’d need a decent sized work-force to produce food for the non food producers such as the political elite. I guess they could get those poor bastards from the tilium ship to till the land. Or maybe they could have kept a few Centurions as agricultural labourers/slaves. Oh, hang on…
See, civilisation might have given us loads of cool stuff, but it has its crappy aspects. It also almost certainly arose as a result of the need to manage large numbers of people in restricted geographical areas using limited resources. These conditions don’t apply on a sparsely populatin Earth, so maybe there’s no point being urban and civilised. Doesn’t mean people have to be stupid. Sure there’s a lot of learning to be done, but maybe they could learn from the natives - getting through the “first winter” and all that. I seem to remember a story about that from our more recent history…
If they did want to start building cities and extracting resources on an industrial scale they’d soon end up separating themselves from those early modern humans, and likely coming into conflict with them, although they could have done so in the uninhabited parts of the world (namely the Americas and Australia).
I think it works just fine as an ending from the technology perspective, although I agree that there might have been more resistance to the idea. But then after years cooped up in the Fleet, maybe people had had enough. Maybe they didn’t have all the luxuries of civilisation to give up in any case - resources were short. Wild game barbecues and sitting about in the sun probably seemed pretty attractive after ship quaters and algae.
I like the poetry of the ending, but then I do have anarcho-primitive tendencies (only tendencies - it wouldn’t be feasible or necessarily sensible or desirable for us to all become hunter gathers).
But there is an irony here. RDM seems to think that the story works with Tyrol fathering the Scots and us all being descended from the population of the fleet, combined with our real palaeolithic ancestors, even though this sort of udnermines the mitochondrial Eve proposition. Of course for the story to work in the context of what we know about human history, and for Mt Eve to be identified with Hera, we know that pretty much all of the colonists, and the natives, must have died out. So their renunciation of civlisation and technology ultimately did lead to their demise, with the exception of the descendants of Hera alone, who ultimately “out competed” their peers, maybe after a period of initial success. Which is sort of a pity.