Here’s a little thought experiment I came up with: let’s say the population of a large city under a communist government was suddenly transported back to prehistoric times. None of their technology came with them, only the knowledge in their brains. Let’s assume they survive, would they be able to keep living under some sort of Marxist-leninist/communist ideology? In the complete absence of technology, do you think a large scale communist society can be maintained, or would it necessarily have to dissolve into something more akin to “tribal communism”? Would the tribes they revert into start warring with each other for resources like actual prehistoric tribes did? Do you think the people in this situation would be able to hold on to communist ideals from a mental perspective, or would people start wanting a capitalist or other system?
This is a pretty fun thought experiment. There are a lot of angles you can approach this from. One of the first things that pops into my mind is the “base and superstructure” metaphor. If we accept the idea that the superstructural realm of culture, politics and social mores is primarily determined by the material base (with some feedback and wiggle room of course), and you completely change the material base which that superstructure is built upon, it will have profound implications. On one hand, you’d have an absolute crisis on your hands, but on the other (at least, in contrast to the present day) you at least wouldn’t have an entrenched capitalist mode of production or the dominance of its ideology to contend with.
The second thing that occurs to me is that no city exists in a vacuum. You could not sustain the 8.3 million population of New York City using primitive agricultural techniques within the geographical confines of the city proper. The population would immediately need to disperse to take up agriculture, hunting and gathering to provide for the basic necessities of social reproduction. If the time-travel were truly sudden and unanticipated, it would be an absolute calamity - the end result could very well be barbarism instead of socialism. If there were some preparation involved, things could potentially go much more smoothly.
Assuming we get past the initial calamity and a sustainable agricultural society is established, I think the socioeconomic theory carried in our time-traveling society’s heads would put them in a better position than if you were to simply take a time machine and select a random agricultural society from history. Marxist-Leninism in particular would probably be rendered largely irrelevant due to the fact that the society is no longer contending with a burgeoning capitalist-imperialist global economic system, but its dialectical-materialist roots would still prove incredibly useful in organizing society as well as predicting/preempting destructive social fissures.