Offline mode using the QlikView iOS app: section access applies the same way as online. It will only slice those contents which the user is allowed to see. The slice happens on already reduced data according to section access.
Offline mode as in downloading the QVW and opening with QlikView Desktop will also work if Strict Exclusion is checked. Before using strict exclusion make sure that it works using Ajax or Desktop with Open In Server.
Yet, if it's sensitive data, I would not allow any user to have access to the files, to start with.