Board Thread:Questions and Answers/@comment-36790992-20180901191429/@comment-36761202-20180906163912

Well... this is just speculation, but perhaps if their Soul Sleep (aka Hakusui) and/or Saketsu, they could. According to the page for the Chain of Fate, 'If [the Hakusui and Saketsu] are pierced, they seal up this spiritual power, and the Shinigami will lose all their power. The Shinigami who experiences this will never be a Shinigami again.' A Shinigami can not fully Hollowfy, as far as I know (unless White counts?) but a Soul can. Though I've never heard of a Soul who's been to the Soul Society ever turning into a full Hollow; there must be something in the Konso/Soul Cleansing process that permanently changes a Soul, or the Soul Society itself does.