I have heard Lord Rama left his physical body and went to vaikunta. So, what is the story of Lord Rama's departure?
Disappearance of Sri RamaChandra is mentioned in many Hindu scriptures. some people wanted to know how Sri Ram died? Death isn't a term which used with Avatars of Vishnu. All Avatars of Vishnu appear to restore dharma and then they return to Vaikunta.
After the successful completion of Ashvamedha Yagna, Shri Rama continued his normal routine of observing celibacy and administration. Shatrughna killed Lavanasura and ruled Madhurapuri; Bharat administered both the banks of River Sindhu and controlled Gandharvas; Lakshmana conquered Madra desha, installed his sons as the Kings and returned to Rama for providing service to him. Shri Rama did Ashvamedha Yanga, after installing a Golden Pratima of Sita; in fact he performed several Yagnas in the same manner. Sage Valmiki exhorted Rama about Sita’s spotlessness and piousness time and again and Shri Rama finally opined that indeed he was fully aware of her chastity and purity but since the allegation came from the Praja (Public), Sita should prove her innocence before the people. Sita then declared in a huge Sabha that if she performed puja to any body else excepting Shri Ram in her mind, thought, tongue or action then my mother Bhu Devi might take her into her mother’s fold. Immediately, there was an Earth-quake and Sita entered into a huge cleavage. Bhu Devi herself lifted Sita into her belly and the great Garuda, the Carrier of Lord Vishnu, lifted her from Rasatala to Vishnu loka as seated on a Golden Throne. After Sita’s disappearance, Shri Rama ruled for eleven thousand years. One day, an old Tapasvi came to see Shri Ram and told him that none should enter his Chamber while he was giving an important message from Lord Brahma in secrecy. Shri Rama called Lakshmana and instructed that none should be allowed to enter as long as he was conversing with the Tapasvi and otherwise that person should be punishable with death. Lakshman himself stood at the door and ensured that none would disturb. The Tapasvi conveyed that since the death of Ravana, Kumbhakarna and other demons Rama was to live for eleven thousand years and that it was time for Rama to leave Earth and return to Vaikuntha. While this secret conversation was going on, Durvasa Maharshi arrived and wished to meet Shri Rama, but Lakshmana declined entry stating that a representative of Brahma was in an important conversation and that he could not see Shri Rama then. Durvasa grew angry and threatened Lakshmana with a severe curse if he did not permit entry. As there was no other alternative between Rama’s instruction and Durvasa’s threat of curse, Lakshman entered River Sarayu, taking his original Swarupa of Ananta Naga with thousand hoods. After the meeting with Kaala Deva in the form of the old Tapasvi, Rama realized that Lakshman also having gone, it was time for him also to terminate his ‘Avatar’; he established Kusha in Kushavati Kingdom and Lava in Dwaravati as their Kings. Taking a hint from Shri Rama, Vibishana, Sugriva, Jambavan, Hanuman, Neela, Nala, Sushena and Nishada Raja Guha arrived. Shatrughna performed the coronatation of his sons at Ayodhya. The rest of them said that they would not like to stay back on Earth in the absence of Rama even for a moment. But Rama asked Vibhishana to continue in power at Lanka for long time and instructed Hanuman to continue on Earth forever to sustain the message of Shri Rama.
The rest of them accompanied Shri Rama into the Sacred Sarayu River. Bharat, Shatrughna, and all the citizens of Ayodhya along with their wives, Mantris, Servants, Vedikas, Brahmanas, the nearby animals, birds, and all other Beings who accompanied Shri Rama never looked back. As Shri Rama went deep into the River, Lord Brahma, Devas, Rishis and all Celestial Beings extolled Raghunatha even as He took the Huge Form of Maha Vishnu with his four hands along with Bharata as Shankha, Shatrughna as Chakra, as also Gada with Sri Devi and Bhu Devi beside Him.