If your Demo Importer is missing from the theme panel, it means that you forgot to install a plugin. The plugin responsible with the Demo Importer feature is ModelTheme Framework.
In order to check if it is active or not, please go to Appearance – Install Plugins: Here you will see a list of plugins recommended by the theme and not installed or activated.
The theme also gives you suggestions that a required or recommended plugin is missing, via this notice: