I have fond memories of ShadowGuard, though it was painfully short. As you said, Werelynx, it's an unfinished story. Such modules, to my mind, should not have been premium modules to begin with.
Anyway, I made two attempts all in all to allow premium modules to be played 100% offline. It's still a nuisance to be required to be connected to the Internet whenever you want to play single-player modules.
I noticed that Diamond Edition premium modules can authenticate offline thanks to small (1KB) .dat files that are installed into the game. I tried some magic to create similar files for other three premium modules, but to no avail. I also tried it the other way, to trick other premium modules into using these .dat files instead of requiring their own ones, but in this I failed as well.
Of course it would be best if they could be decrypted totally, so that they could be opened in the toolset, but I can't do this.
The most optimistic thing I can say in this matter is that it can be done.
I remember someone posting on the old forums a screenshot of PotSC opened in the toolset, but he wasn't eager to share the methods he used or the decrypted modules themselves, for that matter.
To be honest, if we don't count the engine and hardcoded scripts themselves, premium modules are nowadays the last remaining part of Neverwinter Nights that has not (yet?) landed in the hands of the community. We currently have our own master server and patches, but premium modules are still unbreached fortresses that we can neither analyze to learn from them, nor fix some of the bugs they have. I'd guess that nobody really bothers to do anything about them and that's why they remain unbreached. '>