How do the members of the encampment plan to pass on the information found in books?

The members of the encampment store the information from books in their memories, but they aren't certain that the information will ever be passed on. They hope that if they commit books to memory and keep the information alive in that way, then there will be "customers who might come by in later years."
In the final chapter, Granger says that the job of the people in the encampment is simply to remember, so that one day "we'll remember so much that we'll . . . dig the biggest grave of all time and shove war in and cover it up." In other words, the people in the encampment will pass on the information from books firstly by remembering and then by showing these memories to people as and when those people think of doing something bad that has been done, and has gone badly before.
The people in the encampment hope that people in the future will learn from the history that they are storing inside their heads. Given the course of history, one might think this a rather naive hope, but arguably, in the context of the story, it is the only hope there is.