I just tried messing with this, and it might work, but I can only get part of the model into Maya. I'd have some gaps to fill, though it's not like there's a better solution.
Turns out there WAS a better solution: I noticed that, much like the other chewed-up island, Eleuthera is made up of two copies of a different island, scaled and rotated with some parts removed.
So I managed to recreate it by looking at the original world map GM file, and using the in-game archipelago map as a guide to position the island properly.
That's one crisis averted, at least.
For reference, here's how the map is currently looking; no islands moved yet, but the CoAS mainland has been added.
The second image is a comparison showing the in-game archipelago map used instead of the blue sea plane.