What would happen to a Menos or an Arrancar killed with a Zanpakuto?
I don't think it is mentioned anywhere, but what I think would be logical (but does not happen in the anime/manga) is that the myriad of hollows suppressed within a Menos are released (since the dominant personality has been destroyed) while those that were damaged in the process of the attack (e.g. those that constitute the wounded flesh) would be purified. So a large-scale attack that can obliterate a Menos might purify all of the souls.