Yikes! Sounds like a thorny workflow.
Is there some material reason why you need to present a single contiguous document to the copy desk? A series of numbered files wouldn't work?
Is there some reason why you want the copy desk to get HTML instead of, say, RTF?
It is too much of a heavy lift to try to keep the word docs up to date with editors constantly editing, designers editing, etc. Copy desk works in word.
Look into WordsFlow by Em Software.
If I absolutely had to merge all of the Word files for a given book into a single document, I'd use a VBA to do that in Word, and allow InDesign to spit out its default one-exported=document-per-InDesign-story.
Also, instead of using the Book feature, I'd suggest that you look into placing your designers' pages as INDDs into another InDesign file.