There has been some research done regarding the population levels required to support technologies (although I’m blanking on too many details to track it down quickly). The basic point is the more advanced the technology the larger the number of independent specializations required to come together. Areas throughout history that have decreased in population have lost technologies because there weren’t enough minds to support all the information required to maintain its then current level of technology. Books can certainly accelerate re-adoption but the only technologies that will be in use at any given moment are the ones that people are actually fabricating, i.e. the number of people directly correlates with the number of technologies supported. Of course that could all change very soon, and much for the better if our global civilization reached some key technological thresholds before collapse (one can hope the game changing technology could avert the catastrophe altogether). Here’s a detailed look at the rate of technological development. It’s actually not that hard to imagine a point in the future in which the structure of the internet is integrated with the natural environment and self-powered through renewable sources. Significantly more processing power in the decentralized global information processing network (a.k.a. humans) would dramatically increase the rate of recovery and if combined with a certain degree of nanotechnology etc, could actually create a new technological “floor” that would be much harder to fall through.