Two recent publications provide some interesting ideas how knowledge can be maintained over a long period. John Cisne developed a population ecology model of medieval manuscripts. Manuscripts are copied manually, and more popular books have more chance to be copied. Cisne used concepts from population ecology to understand the paleodemography of the manuscripts and conclude that the leading technical titles who circulated in Latin probably survived. See also the commentary of Gilman and Glaze in the same Science edition.
We write only once a sentence that maybe read many times. Changizi and Shimojo analyzed the complexity and redundancy of characters of more than 100 languages. They conclude that the characters are constructed on average by 3 strokes, and that this is 50% redundant. The explanation for this is that characters are still correctly classified (by reading) when errors are made (by writing).