Keep in mind that there is such a thing as a ChoiceScript commercial license:
I know that this isn’t exactly the same thing (the ChoiceScript commercial license is for selling ChoiceScript-based IF not through CoG, as opposed to what you’ve proposed), but even so, I suspect it’s possible that CoG would be open to an arrangement allowing you to sell a version of your originally-Hosted Games-published story on a competing platform if you were happy to sign a contract allowing them to take some % of gross. But as always, you’d need to drop them an e-mail.
If you just create a game using ChoiceScript but don’t publish it through Hosted Games or Choice of Games, I don’t believe the “exclusive license” thing comes into play. (Though you would need to arrange a commercial license with CoG if you wanted to sell any version of your game that is implemented in ChoiceScript.)