Dr. Neville Whymant
One of the proofs that people who have left the Earth plane are alive and well in the afterlife is that people whose bodies have been dead for centuries or millennia communicate through mediums and people who have undiscovered medium abilities speaking languages the person receiving the messages have no knowledge of. Some examples follow.
A Medium Speaks Ancient Chinese
One of the proofs that mediums are receiving messages from people alive in the afterlife is that they sometimes speak and understand messages in languages not known to them, demonstrating that they are in contact with speakers of other languages whose bodies have died.
Dr. Neville Whymant, a British professor of linguistics, was a specialist in languages who knew 30 languages. He attended a séance at the home of William Cannon, a New York City lawyer and judge, performed by medium George Valiantine. In the séance, a man came through speaking ancient Chinese. Whymant knew modern Chinese and knew the literature of ancient China, so he was able to interpret it as perfect ancient Chinese. He learned that the speaker was Confucius, whose writings Whymant knew well. He asked the speaker, in Chinese, about poems people had puzzled over for centuries that Confucius had written. Before Whymant could finish the poems, the spirit spoke the remaining words. Confucius then explained the errors in copying that had occurred after his death, solving the puzzles. 
Confucius had survived the death of his body in the fifth century BCE and continues to live nearly 2,500 years later.
A Girl Receives Messages in Ancient Egyptian
In 1931 a young English girl named Rosemary began to speak in an ancient Egyptian dialect under the influence of the personality of Telika‑Ventiu, who had lived in approximately 1400 BCE. In front of Egyptologist Howard Hume, she wrote 66 accurate phrases in the lost language of hieroglyphs and spoke in a tongue unheard outside academic circles for thousands of years that was verified by Hume. The accounts are in the files of the Society for Psychical Research. 
In this case also, the ancient Egyptian demonstrated that he survived his bodily death 3,400 years ago and continues to live in the life after this life.
A Housewife Writes in Perfect Middle English
Pearl Curran, a housewife from Saint Louis who was barely literate, began to write in astonishingly accurate Middle English. Under the guidance of a spirit entity named Patience Worth, she produced sixty novels, plays, and poems, including a 60,000-word epic poem, all in perfect Middle English, a language Curran could not have known.[i] Patience Worth survived the death of her body and was intellectually and artistically vibrant 500 years later.
The fact that the messages came through in languages the mediums did not know demonstrates that they originated from the personalities living in the life after this life and that the mediums were not psychically reading someone. There was no individual related to the people in spirit present when the messages came to the mediums. 
 Nandor Fodor, These Mysterious People (London: Rider & Co. Ltd. 1934).
 Richard Lazarus, The
Case Against Death (London: Warner Books (1993): 85.
 Lazarus, The Case Against Death, 19.