It could stand up independently. Currently the characters have only been told of the invasion, and they see the ships entering Insomnia, if/when they go back to Insomnia everything will become contextualized (in terms of it will no longer be second hand information). Other than that, Kingsglaive provides no real insight into much else, which leaves the game to develop the plot and characters itself. Other than that, I think Brotherhood provided some great insight into the characters, but It seems like the character interactions are making up for it in game, so even without Brotherhood its all being conveyed in game correctly.
On another note, 5500 Followers needed for the Moogle Movie. Do you guys think that they recently reordered the whole thing so that they would be able to get the movie out in time for Paris Games Week?