Low-tech wins this one.
The book will never be replaced. Oh, they may stop publishing, but that will be because people no longer read.
Anything electronic is too awkward to manipulate easily, too fragile, to dependent upon a chain of support to keep it going and alive. There will have to be leaps in technology for those things to be reliable enough.
Throw a book in a backpack, suitcase or hip pocket and you've got a friend just awaitin' your pleasure. You know it will "work".
Arf