The short answer is: "we don't know." The original plan was to make it require the original game,
however that will introduce several complications (for example, we won't be able to distribute a trial version),
and also the development of warband has surpassed the original game budget-wise.
Therefore we are considering making it stand-alone.
In any case, we'll most probably make a discount for players who bought the original
(at least from our online store) and recommend other channels to do the same thing.