OK, I'll see about getting this on track.
There's nothing stopping anyone from going ahead and attempting this, and completing it. If you're content to keep it on your machine, i.e. not publish it, then have at it. 
It would be a good way to work up some ColdStone chops if you don't have a finished game yet.
However, if you do want to publish it, you have to ask various people for permission, and you might as well do it at the outset to save yourself the labor if one of them says no. I'm not exactly sure who to ask, since I'm at work on a Windoze box :frown:, but the publisher (Ambrosia, obviously) and the people listed in the game credits (e.g.: Glenn Andreas, and the guy who did the music if you want to borrow that as well) would be a good start. Glenn/Ambrosia might be able to claim character copyright on the principle characters, so you probably can't just pick Hector and Alaric and company up and plop them down in an all-new place named Zithera and expect to get away with it. 
Now, if you decided to base a tale around saving the underwater realm of the Sea Queen Cirala, that might work.
There wouldn't be much point in just doing the game over, obviously, so what could be different? Besides fleshing out the landscape, that is. You could add boats to reach nearby islands, and guide characters, rope and mountaineering skills so that the mountains aren't just a big impasse. The combat engine and spell system might have to be totally reworked if ColdStone goes real-time. It looks like Coldstone is more immersive than Delver, which means you'd need to replace all the little windows and boxes (which I got fond of for managing a lot of things at once) with a more conventional interface.
Would it be veering off-topic to proffer plot ideas for a potential Cythera II, assuming for the sake of discussion that the developer had been given the green light? I've got a few ideas that I'd be happy to share.
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James
dystopia, n.: A utopia, in practice.
why are we living surrounded by such animosity ???