When you donate an item to a library, archives, or other facility, ask them about their retention policies.
Can they afford to maintain the item? What happens if they are unable to afford to maintain it as a part of their collection? Does the library, archives, or other facility have an actual interest in your material? Is there something about it that is unique and worth collecting? Is your material simply a collection of photocopies of public records or is it personal family letters or other unique material? If you self-publish your biography is the library really interested in having it on their shelves? If your donated material is not used will it be culled from the collection?
All questions to think about.
Libraries, archives, and other facilities cannot necessarily keep everything forever.