If we were to get back to those self-sufficient, egalitarian communities, how on earth could we at least keep that level of technological development we reached today primarily due to division of labor (which is impossible without building social hierarchies)?
We couldn't keep it. But we can't anyway. A society is something that always disappears by collapse. It is growing rampant endlessly, until the end. Societies are 'problem solving societies' (Tainter) which are permanently investing in additional complexity to solve the problems.
The Game is over as soon as the ever shrinking marginal return of additional complexity reaches the tipping point.
It is an interesting point that tipping point. I think you could be right but for a possible qualitative leap, i.e. is a major and sudden change in social structure or something related to it (and this definitely won't be towards self-sufficient, egalitarian communities). I am not that much into sociology and that kind of things, but at least I can explain how it happens in economics and why we are still advancing in technology...