This is only a cosmetic effect, and does not remove the dark sigils from the inventory of the player. Upon completing a new game cycle, all key items are removed from the players inventory, including dark sigils. If the player uses a purging stone acquired on a previous playthrough, they will no longer accrue hollowing until levelling at least once with yoel, gaining them a dark sigil in their inventory again. If the player has a hollowing stat of 15 or greater before speaking to yoel due to a previous new game cycle, they will be able to recieve all 5 dark sigils in sequence, without needing to die in between. Following this, yuria will then spawn in firelink upon reloading the area. Hope this helps!