This also gives me a chance to ask, you want the dutch wiped or capulated?
Your question is an important one, particularly if it is for your first Vassal.
You have to ask yourself a few other questions to get your answer:
1. How badly do you want said AI's remaining Cities?
2. Can your current military forces push on easily or are they wounded and in small quantity?
3. In 10 turns, will your forces be in position to attack again or will you still not have sufficient forces and/or want to have your forces deployed to another part of the world?
4. If the AI that you are attacking is Pleased or Friendly toward another AI, can you accept your war target Peace Vassaling to said other AI and potentially getting some free techs (such as Rifling) in the intervening 10 turns? In particular, can you see yourself winning a war against the strongest AI that your war target is Pleased or Friendly toward as well as your war target, starting 10 turns from now?
5. Do you hope to win via the Apostolic Palace or the United Nations without killing a lot of other AIs?
6. Do a lot of other AIs like (Pleased or Friendly toward) or dislike (Cautious, Annoyed, or Furious toward) your war target?
7. Do you have sufficient military forces to garrison in any captured City which will be oppressed by the war target's Culture between now and the time that you can feasibly declare war and win against them and their future Master?
8. Do you already have other Vassals? Usually, particularly for Apostolic Palace and United Nations victories, you either have 0 Vassals or a ton of Vassals.
Answer those questions and you'll have a clearer picture as to whether or not to take on the Vassal.