An interesting problem and hoping to see a good solution.
For the record (others reading this thread), when the Navigator is Open showing by Headers, you can search any word or phrase and the chapters containing that Word or Phrase will be Highlighted.
It would be ideal if Word allowed the Chapter Reference(Chapter/Heading# by Selected Heading Level) to be listed when creating the Index. OR if Word allowed Section Breaks as a property of a Style (like Page Breaks Before is allowed.)