When using RADIUS or LDAP authentication, if you want to ensure that some or all administrative users are always able to manage the network security appliance, even if the RADIUS or LDAP server becomes unreachable, then you can use the RADIUS + Local Users or LDAP + Local Users option and configure the accounts for those particular users locally.
For users authenticated by RADIUS or LDAP, create user groups named SonicWall Administrators and/or SonicWall Read-Only Admins on the RADIUS or LDAP server (or its back-end) and assign the relevant users to those groups.
For RADIUS, you probably need a special configuration of the RADIUS server to return the user group information.
For how to configure administrators when using LDAP or RADIUS, refer to Configuring Local Users and Groups.