The POD is that Balthasar Gérard dies before getting to assassinate William the Silent. Result, William doesn't die and get's to live to an cranky old age and the weakening of the stadtholdership which took place after William's death in OTL never happens, derailing the rise of the rich citizen and merchants class to their OTL dominant position. The Netherlands eventually are divided into four Bundes-nations (?). Furthermore, the Netherlands fail to seperate from the Holy Roman Empire after the Peace of Münster.
This is my speculation on what could happen if William the Silent survived. What's your opinion?