If it's properly packaged and sealed who knows, maybe 200 years or more. Maybe on the more side as we have recovered items from 200 years ago that didn't have any protection and we still know what they are.
With the dessicant, cosmoline and a vacuum sealed bag.....anyone got an idea?
A collector turned me onto using carnauba-wax based paste floor wax for long-term storage. Collectors want to clean their high-end weapons as seldom as possible, but definitely don't want them to rust - yet don't want to glob them full of cosmoline, either.