His first wife, Luisa Maria Gabriella of Savoy, died at the age of 26, after giving birth to four children. The Spanish loved her, nicknaming her 'la Saboyana', and she was rumored to be the real power at court, dominating her husband who was madly in love with her.
What if she had lived? Of course, it removes Isabel Farnese from the Spanish scene, but I feel it also alters the entire future of Spain, since none of her children left issue.
Discuss.
First off, the Princesse des Ursins remains the dominant person in Spain until her death in 1722. Luisa Maria and Felipe both loved her but only the former was strong enough to protect her. Felipe bowed quickly to the faction who wanted to get rid of her.
As to children, Luisa was only 26 (oddly and creepily the same age that her sister Marie-Adelaide, her aunt Maria Luisa and grandmother Madame died at) and had gave birth to Fernando not even 6 months before her death. Its pretty obvious she and Felipe would have more children.
Third, Luisa, unlike her successor, was popular and enjoyed good press in Spain. So, she'd be in a similar position to Elisabeth Farnese, only with support among the Spanish elite. The real question is would she attempt to restore Spain's power in Italy? Her children wouldn't have a claim to Tuscany or Parma and Sicily was ruled by her father the Duke of Savoy. So, I think we'd see Spain make a grab at some point for Naples and Sardinia, Sicily is going to be the real question.
On the other hand, Duke Vittorio Amedeo cared more about gaining the Duchy of Milan in its entirety (something he was sort of promised and was then screwed out of by the Habsburgs). So we could see a deal between daughter and father: ally with us and we'll help get you the rest of Milan. In exchange you cede Sicily. Hell they might throw in Sardinia so Vittorio can remain a King.
The real question is timing. The War of the Quadruple Alliance, Spain's first attempt to regain their Italian possessions, was fairly well planned but had horrible timing. Luisa, having been Queen for over a decade, might be more patient then her successor and more willing to play the long game. If Spain waits and allies with France after the Duc d'Orléans dies/falls from power or at the very least secures French neutrality, then things are different.
French neutrality means the the enemies are Austria, Britain and the Netherlands (the last of which isn't much of a player). Add to that a Spanish-Savoyard alliance and we could see an early version of the Polish succession war, only with Spain gaining Naples and Sicily directly instead of enthroning a second/third son.
Could be very interesting.
Well, that wasn't really her fault, don't you think? Only two of her four children survived to adulthood. The eldest one died aged 17, and his wife wasn't even 14 when he died. They didn't even had the time to really try to have children. The other, Ferdinand VI, we'll never know if it was his problem or his wife (who only had a stillborn child in 1733).
Maybe if Luisa Maria had lived she would have more children, and eventually one of them could have heirs.
I'd say the problem was both Fernando and Barbara. They probably had trouble conceiving in the first place and the 1733 miscarriage rendered Barbara barren.