eugh... I hate the GF stuff. Not because "amnesia" is an overdone plot point and ... but because you never really interact with any of the GF's; literally it is turning a battle component into a plot device (I don't think they actually give any indication of in-plot moments where they can't remember shit either with their recent use of GFs, nor is their memory only "foggy" than completely forgotten upon meeting each other*). If FF9 pulled it off, I'd believe it better because a Summon is in about half of the FMVs.
And I like the theory about Squall is dead (or the similar one spelled out for Zelda: Majora's Mask) -- but I can't imagine it being what the creator or writers had in mind beyond awesome coincidences. And like Mongoose says, it's a good coverup for otherwise bad storytelling. I dare a plot to pull that off though.
The Descent pulled this off. It wasn't a "she was dead" the whole time thing but a twist in that she "thought she was saved"..only to cut to her imminent death.
* If I'm wrong I"m sorry, it's been a while.