Let's say that something like a wooden bow is kept in the perfect environment. A cold, dry, oxygen depraved environment where no chemical reactions could possibly happen besides the reactions of the bow itself, I believe (if my chemistry classes served me right) that the only way the bow could possibly not survive is after going through several half lives to the point where the elements that form that compound of materials no longer share the properties that allow it to hold together. Thus it would be dependent on the half-lives of the materials involved.

BUT, as an idea, some materials you'd expect to decay have been found in excellent condition. Some good examples are a German tank pulled out of a bog (a relatively oxygen deprived environment) in near perfect condition and the wreck of the Mary Rose, an English ship carrying archers which had capsized in 1545 being recovered and finding 137 surviving longbows. Despite the tank being in a bog for nearly 70 years and the longbows being locked in chests for 500 some years, both were kept in conditions that kept decay to an absolute bare minimum, and when half lives are of relatively stable elements like iron and carbon which last millions of years, well, it'll take a very long time