If a volume is no longer available but still shows in ShareBrowser Client, it's typically expected behavior as a result of at least one file on the share having been indexed.
Much like a USB drive that is indexed by a workstation and then ejected, the contents of the drive remain searchable in the ShareBrowser database even after the disk is removed. As far as the database knows, a deleted share is just an offline volume that may one day come back online.
To remove unwanted volumes, open ShareBrowser Admin, select the volume(s), and then click "Volume Maintenance" - you'll then see the option to delete the share.
This only removes the index information; it does not affect the contents of the shares, but note that any custom tags or comments applied to the media on the share will be removed. The metadata can first be exported (and imported) in ShareBrowser Client by right-clicking the volume or any of its contents.