【How-to】How did vibhishana died - Howto.org

Due to Vibhishana’s differences with Ravana, because he was against the act of kidnapping Sita and most of all because Ravana wanted the throne for himself, he fled Lanka. His mother, Kaikesi, advised him to go and serve Shri Rama, who was at that time assembling an army to conquer Ravana and to recover Sita.