How do you deal with no-magic areas when you want to play a magic-user?

There is a critical storyline quest under castle stormfist which disables magic, and the finale of the game disables magic.

If you are playing a magic-user, what exactly are you supposed to do?

And for that matter, how are you supposed to know that you need 4 levels of pick pocket to get the 'underneath castle stormfist' portion of the story unlocked? Was there meant to be another way here? Or do you just have to know that you must take the 4 ranks in order to finish the game?