Does this mean you can't do GalCiv 2 again even if you wanted to? Is that why you are so stuck with using Steam? You sold off both an important team and rights to important code? It sounds like you cut off and sold one of your arms.
If Gamestop had done something with it instead of becoming some kind of Steam franchise... Or if EA had managed to do something with their Origin...
What I do wonder is how expensive in time and money is to develope a new Not-Impulse. You can use Steamworks features no matter the engine of your game or what kind of game you make. Impulse was supposed to be similar in taht regard. So while creating a new one would be expensive (or not cheap at least), in the long run you could use it for all your games and retain more control over your product.
I do admit that I'm quite ignorant about the inner details of what Steamworks really imply so keep that in mind when thinking about what I said previously. Stardock is no super duper small indie that only makes money from a game once in a long while so maybe I have the false impression that if really wanted (and circusmtances allow it), they could do it again... but this time just for their games and not to create also a digital shop. Or hell, where are the phylanthropists? We need an open source one to rule them... er... as alternative.
I do think that Steam is a good service. Really good. Unfortunately, too good compared to what competition offers. But I only support those Steamworks games that I really think that are awesome for me. XCOM:EU and its hundreds of hours played are evidence to me. I expect the same from this game, offline mode or not. We will worry about the Windows emulator, the Steam emulator and the game in 20 years, huh?