Is not forgiving a brother who assaulted me with beating and verbal abuse destructive to the reward of the 15th of Sha’ban night?

If your brother insults the religion, this is an act of disbelief that expels one from the faith. Shunning him is permissible as long as he remains in this state, because shunning here is for a religious matter, not for worldly affairs. It is even more appropriate if there is hope that it will lead to his rectification and repentance, alongside enjoining him to good and forbidding him from evil.