why the hell would you need internet?
its not an mmorpg
If the game requires Steam, then you'll need to activate it using Steam, which requires an internet connection. You can, of course, play it in offline mode afterwards, but you'd still need an internet connection to be able to activate it, and there have been single player games that require Steam, like New Vegas, for example.
Thus, as of now, we simply don't know the answer to this question. We can only guess based on Bethesda's recent decisions at this time, until Bethesda says whether it will or will not use Steam or any other form of DRM that requires online activation, and that's the only reason I could see the game needing internet access, because of course it's not going to be an MMO. Though considering that Fallout New Vegas used Steam (And while that game was developed by Obsidian, since it was published by Bethesda, I'm sure they're the ones who made the choice.) I wouldn't advise getting too optimistic if Skyrim requiring Steam would stop you from playing it, but we don't know yet of course, so I'm not saying it will certainly use Steam, or any other form of online activation, I'm just saying that I think it's very much a possibility.
And I think the existence of threads like this shows why making Steam mandatory for playing the PC version of the game is a terrible idea.