If they know or have been informed about it, yes. Distributing illegal goods is no minor offense. The argument is often that the store (owner/operator) was not aware of the fact fact regarding the sold product and that he was in the right assuming the product was legal. If however the illegality is obvious or has been brought to the stores attention it cannot be sold any longer without significant risk of legal consequences. At least that is the case here (Germany).
Regarding the addon in question here, it is known and only the direct prove of it has been wiped by the creator of the addon. Which in m eyes should raise more than a few eyebrows if I would operate the store. I would not touch a product with former intellectual copyright infringement with a ten foot pole.