For sharepoint linked libraries, there should be a setting that allows access to file in online only mode, meaning files are not stored locally .. if there connection to the internet then live synch is active otherwise files aren't available for synching. Files access works the same way windows explorer opens files, and warns users that file is in use, and allow collaboration. Avoids multiple copies of the same file being stored locally by multiple users and creating very annoying upload issues and synching problems.