I was always under the impression that the original 1.0 storyline would have had some kind of similar Calamity befall Eorzea..nothing large scale like Bahamut, but enough to risk the safety of the towns and whatnot. Maybe the awakening of all the Primals, and the Garleans waging war against them or something?

As for Courgevais, I seriously doubt he's the Garlean spy. It's too easy. The only thing that is certain is that he knew Warburton, and speaks as if they were old comrades...and we know Warburton and Ascilia were from Ala Mihgo.

I've been rewatching the story in French to see if I can glean any extra tidbits (I've done this after realizing discrepancies between localizations when all the ruckus over the Commemorative Coin came up XD)

Starting here:
http://youtu.be/2mHD3cSMYWs?t=1m50s

Courgevais says, "L'Empire? ...Imbecile." (The Empire? ...Idiot (fool, imbecil)

Then Ascilia follows with "Ce n'est pas l'Empire! C'est quelque chose de bieeeen plus effrayent!" (It's not the Empire! It's something even scarier!)

In the English text, Courgevais simply just says "the Empire?" which can be ambiguous sort of..but the French text, by adding the word "imbecile", he quickly dismisses Nielle's words as folly.

Of another note, although it doesn't affect the overall story, Ascilia's words to F'lhaminn (the same cutscene) are somewhat different:

English:
Ascilia: You...You killed my father? It was you? How could you!? Get away from me! Just leave me alone! You...you murderer!

French:
Ascilia: Je ne veux plus te voir! Je deteste cette Cite! Je veux rentrer chez moi!
(I don't want to see you! I hate this city! I want to go home!)