Was World War I a preventable war, or were the nations of Europe committed to fighting even before the assassination of the Archduke Francis Ferdinand? Can you envision a realistic scenario by which the outbreak of war might have been averted?

Yes, World War I could have been prevented and spare many lives of men. The assassination of the Archduke Francis Ferdinand pretty much started it, so if only the assassination did not happen, there might be no World War I. Also, if only the allies did not step in and also declared war with other nations. However, the thing is the countries were already building their military forces that may be triggered them to declare a war.