I was listening to Ray Harris' History of WW2 Podcast, and Philippe Petain came across to me as purposely subverting the French war effort against Germany.
For how long had he planned to be head of Vichy France? Did he have any journals, diaries, or correspondence that indicated a desire to do this before the surrender? Is there any evidence that he was, in fact, purposely trying to make France lose to the Nazis?
I don't really know that Petain was trying to make France lose, you might want to clarify that part. The French lost when the German armoured spearheads reached the English Channel and cut of a good portion of the French Army in Belgium and northern France. Shortly after the French government fled Paris, Petain began to draw up proposals for an armistice. After the French government, Petain stepped up to lead the country and signed a peace treaty.
Petain had two goals, one to prevent France from losing more territory, men, independence than was absolutely necessary, and two, he wanted to prevent communists and other radicals from rising up and causing civil war or civil unrest. Petain wasn't power hungry, he wanted to try and lead his country through a tumultuous period. He ended up collaborating with Germany because in 1940 they looked like they would win and Petain wanted to make France suffer as little as possible.
Now the French State or Vichy was a very authoritarian, paternalistic dictatorship. But that was more because Petain was an old school French army officer who felt that the country needed a firm guiding hand.
As for the original question about how long Petain intended for his dictatorship to last? As long as necessary, thats a very vague statement, but that was the point. France was completely destroyed by the war with Germany and needed to be rebuilt.