Wouldn't they? They didn't revolt because Philip was Spanish, they revolted because they weren't allowed to be protestant and because the Spanish wanted to take away Dutch autonomy. Wether Spanish or Austrian, the Dutch will go protestant. This could still cause a conflict with the Austrian Habsburgs. And if the Austrians would leave the Dutch alone, I suspect that within decades all of the Dutch speaking Netherlands and a significantly portion of the Walloon Netherlands would be Calvinist. It was a conversion from the bottom up, not top down.It was truly the people, the common people who converted and manage to take over in the cities.
I have to dissagree here. The religious situation at the beginning of the dutch revolt is that the majority of the population was undecided in it's religion. There wasn't a yet an all clear distinction between what was considered calvinist and catholic and most believers followed someone they considered an authorithy in this. F.i. in the village Lexmond (ZH), there was a catholic priest who around 1600 broke with the bishop, switched to the protestant believe and as a consequence his successor was also calvinist, this time educated in Leiden. The population in Lexmond became as a consequence also calvinistic. In another village Hagestein not far from there, the priest remained catholic, when he died the Kapitel van Oud Muster in Utrecht appointed a calvinist successor for the parish, but that person switched back to the catholic faith and as a consequence Hagestein remained mainly catholic
Another example of the fluidity of religion is a priest in Houten(UT), who asked around the same time his parishioners in which rites they wanted their children baptized, the calvinist or the catholic.
One of the main factors to determine if a region stays catholic or switched to calvinist is a succesfull implementation of the reforms of the council of Trent. And specifically the appointment of seminary educated priests in the parishes. This failed in the Republic for obvious reasons and even there there remained strong catholic enclaves in the countryside, like in the area above Alkmaar and Volendam. These enclaves have been explained as a consequence of the allowance by the local ruler of (missionairy) activities by the catholic church in the early 17th century. This principle also explains why Brabant and the Achterhoek remained catholic even after conquest by the Republic.
This all makes me believe that a Netherlands not afflicted by revolt would slowly be turned catholic, just like f.i. Poland, where the counter Reformation was also succesfull in reconverting.