Let's say Queen Mary II's reproductive organs don't fail at their biological function and good ol' William and Mary end up with a lovely and healthy baby boy. Now what? This may mean a continuation of the personal union between England (possibly soon to be formed with Scotland into Britain) and the Netherlands. I don't know about what a possible later female monarch getting the crown in England would do in Netherlands, but let's just handwave it by saying that the political entanglements means that the Netherlands will just accept it. It may not even come up at all but the English allow female monarch if there are no male heirs in the way so it's something that you have to prepare for just in case.
Hanover was in a personal union with Britain for over a century and all it took was one of those aforementioned female monarchs to separate them. The political climate just wasn't right, and they had little to no cultural effect on each other by the later stages. Would something like that happen to the Netherlands? Would the British come to see them as an unimportant piece of land filled with Deutschemen, or worse, Continentals? Or would there be cultural exchange, cooperation overseas in colonial ventures, linguistic or even population exchange? Or would the differences in British and Dutch culture and politics drive apart the personal union prematurely?