People don't forget, and every civilization has built on the best it found in the ashes of the old.  Should ours collapse and should the survivors revert to an economy that can use no more energy than the sun, wind, waves, and hands provide, that does not mean our science, art, philosophy, etc. would disappear.  The sheer volume of written material out there, scattered across the globe in both printed and digital forms, is so massive, that it would be impossible to lose everything.

Just because said future society would not have the means to build or run a facility capable of mass-producing microprocessors does not mean that nobody would ever again have a microprocessor.  It's rather remarkable what people can hand craft, given the time and the knowledge.  Should the demand for cost/time efficiency be dropped, there is not much in the modern world that could not be remade by small groups of craftspeople.