Hi Blackshirt,
Demonology, Necromancy and Chaos Magic are all on the 'critical' list in terms of stock right now - in fact, last I looked, Necromancy had just 79 copies left. Not enough to fulfil a typical month's sales!
In some form or other, you will likely see these rules appear again in the future, either revamped or compiled, though it will likely be a year (at least) before this happens.
Not on the critical list yet, but moving on to it in the next 2-3 months will be Constructs, Battle Magic, Elementalism and Enchantment. To give you some idea, books typically spend 3 months on the critical list before completely selling out (this information actually goes out to distributors and some retailers - you can pick it up on our mailing list), so you have plenty of time with those titles. Worth keeping an eye on, however, as the Encyclopaedia range does very well in the backlist - we try to print to compensate for that, but we have been caught out in the past!
Hope that helps,