There is no penalty for not completing a BF quest, other than missing the experience points.
Are you sure you sold the pair of green shoes that the quest referred to? They would have been found on the third level of one of the dungeons. In the main game you can not sell quest or unique items (in the act they are found), but I am not sure about the BF quest items (didn't do any of the dungeons or quests). Even if you can sell them, I would think the merchants would hang on to quest items.
Since the BF quests and quest items are randomly generated, there would be no way to cheat to replace a quest item, unless you had an old save where you still had it.
