That is an interesting question. Assuming Antwerp doesn't fall like OTL, Antwerp probably be the Dutch capital. Assuming large parts of Flanders and Brabant are Dutch and actualy remain protestant (they were before being reconverted by the Spanish) they would have been a major influence in the netherlands. OTL the Netherlands was ruled by Holland. Holland would still be a major power within the Netherlands (although far weaker than OTL), Flanders and Brabant (mainly) Antwerp would balance Holland's power, which is probably a good thing. The country would probably still be a decentraliced confederacy, with most power in the hands of the provinces and/or cities. it might still become a republic. The political situation in the Netherlands was pretty good for a republic, so unless they offer the throne to England or France and they accept it, I think a republic is likely. The office of Stadholder would probably still exist, but I think it is unlikely any stadholder would gain as much power as the stadholder of Holland OTL. Good chance the house Nassau wouldn't be the only one to have stadholders. It might even not end up hereditary.