Answer by Raakhee V. Menon:
Thank you for the A2A.
Vibhishana is one of the seven main chiranjeevis or immortals of Hindu mythology, the others being Hanuman, Ashwathhama, Mahabali, Kripacharya, Parashurama and Vyasa. His name is also part of the famous Hindu mantra which contains the names of the seven chiranjeevis and is chanted for luck and longevity…
अश्वत्थामाबलिर्व्यासोहनुमांश्च विभीषण:कृपश्चपरशुरामश्च सप्तैतेचिरंजीविन:।
|| Ashwathaama Balirvyaaso Hanumanshach Vibhishanha Krupascha Parshuramascha Saptaitey Chiranjivinaha ||
Vibhishana is, however, not a complete chiranjeevi as he was granted the boon of immortality until the end of the Mahayuga.
This is why he was still the King of Lanka when Sahadeva pays a visit.