Let's say, for some reason (like the Spanish Habsburgs realizing that uncle marrying niece-many-times-over isn't conducive to the prolonging of the dynasty) that the Spanish Habsburgs last long enough.
And somehow, let's say that it's the Austrian/Imperial branch that got the short end of the stick TTL, and go extinct sometime in the 18th century (which they kinda did OTL).
What happens then? Is the War of *Austrian Succession gonna play out differently?