If AutoCAD DWG Launcher is set as the standard program for DWG files, it automatically starts the correct application (AutoCAD or Inventor) depending on the source application of the selected file when you double click a DWG file. At the moment, no application is opened at all if Inventor is not installed and you double click an Inventor DWG to open it.
If no Inventor is installed on a client, but only Inventor View, AutoCAD DWG Launcher should open Inventor DWG files in 'Inventor View' (if installed).