Is it permissible to cut off ties with a brother who violated his niece's honor when she was young years ago, despite being warned?

Allah has commanded the joining of kin (Silat al-Rahim) and forbidden its severance. However, it is permissible to abandon (hajr) kinship when there is a legitimate religious reason, such as committing a sin or innovation (bid'ah), while observing what serves the greater good (maslahah). The rulings of Hisbah (enforcement of public morality) and Amr bil Ma'ruf wa Nahy anil Munkar (enjoining good and forbidding evil) pertain to an existing wrong, not something that happened long ago or whose perpetrator has repented. One of the conditions for enjoining good is that the wrong be currently present. Abandonment (hajr) is a punishment and a deterrent for the transgressor, and a fulfillment of the duty of enjoining good and forbidding evil. The consideration is the current state of the person, not what has passed.