Leo Depuydt offers some interesting insight into the length of time a manuscript might survive. The following footnote appears within his excellent catalog of the Pierpont Morgan Coptic manuscripts.
"An example of how much time it took for books to deteriorate is provided by a codex described as Nos. 144 + 411. This codex can be dated with reasonable certainty to the first years of the tenth century AD. For its upper pastedown were used fragmentary leaves taken from disused codices and containing colophons dated AD 856 and 868. These two codices had therefore fallen into a state of disrepair in about half a century."
Catalogue of Coptic Manuscripts in the Pierpont Morgan Library (Louvain: Peeters, 1993), L, fn. 30.
J. P. Morgan purchased what are now known as the Hamuli codices. Many of these manuscripts were recovered in almost perfect condition in 1910, and now are the best examples of the bindings used in ancient codices from this period. Ironically, we probably owe the survival of these manuscripts to a persecution which occurred under Fatimid caliph al-Hakim bi-Amr Allah in 1012/1013, as monks appear to have hid them in a stone cistern in anticipation of their monastery's impending destruction. A Fayumic colophon in a Bohairic manuscript (P.Vat.Copt. 68 f.162v) dated to 1014 suggests as much (Depuydt, cxvi).