I definitely mean independent Netherlands. I can see it necessary to be weakened to enable inclusion but I'm not convinced destruction is necessary. Perhaps encirclement.
The Netherlands must be made completely irrelevant. During the 17th and 18th century the Netherlands was one the most important and strongest countries in Europe. Even at its weakest, at the end of the 18th century the Netherlands was stronger than most other European countries. Sure, itcouldn't play ball with the big guys, Britain, France, Austria or even Spain or Prussia, but it was still far stonger than almost all other German countries or Scandinavia or Italy, etc. Simply put. The Netherlands was too strong and influential. There was nothing Germany could offer to the Netherlands. The Netherlands had already formed its own seperate identity (which happened in the 16h century and the roots of it were formed during the middle ages). You must find a way for the Netherlands to look towards Germany, which it won't as long as it is strong enough.
Basicly the best POD would be a Netherlands that remains part of Napoleonic France, but gets liberated (together with the Rhineland) by a young Germany. Or maybe the Dutch Republic is destroyed by France during the year of disaster. France annexes the south, the northeast becomes part of Münster, England gains a couple of trading ports. The Netherlands loses all colonies, etc. The republican government is replaced by a French puppet. This is basicly the point were the Netherlands would start looking to Germany. Although with France dominating Europe, i doubt Germany would form.
Or perhaps change Netherlands' political structure (the merchantile Republic, Stadtholder, provincial autonomy, etc) so much that enables it to be dragged into Holy Roman affair irreversibly. Perhaps through personal union ?
You realy need to change a lot. I think that even if Willem II would manage to become king of the Netherlands, he would look south rather than west. Also you have to realise that the Netherlands would probably dominate any personal union completely. it was way stronger than any other protestant power, with the exception of Britain. Ok, maybe also Prussia, but they would be equal powers instead of the Netherlands being dominated. It is more likely for the Netherlands to draw German states away from Germany than they drawing the Netherlands in.