All this changed Dr. Kotnis profoundly. In his letter to Dr. Basu, who was also on the medical team, he wrote with excitement that he had been "experiencing a good deal of transformation" in his "character" and "ideas", and that he had gotten rid of his bad habits, including his "bourgeois ideas". When the Indian government sent a telegram to the battlefront, urging him to return, he pled with the local officials in charge to let him stay. He noted that the war against Japanese aggression led by Mao Zedong and the CPC was a great fight. He had fallen in love with the cause of the CPC and the base areas behind the enemy lines, and no matter what may come, he would fight together with the Chinese till the final victory is secured.

On July 7, 1942, Dr. Kotnis became a proud member of the CPC and one of the proletarian vanguards. After joining the Party, he devoted all his time to saving lives, despite suffering from pain and illness himself. On December 9, 1942, worn out by overwork, Dr. Kotnis passed away in illness on the Chinese soil. He was then at the age of 32.

In his eulogy, Chairman Mao Zedong wrote, "Dr. Kotnis, our Indian friend, came to China from afar to assist us in our War of Resistance. He worked for five years in Yan'an and North China, giving medical treatment to our wounded soldiers and died of illness owing to constant overwork. The army has lost a helping hand, and the nation lost a friend. Let us always bear in mind his international spirit."

Though he was a CPC member for only three months, Dr. Kotnis dedicated himself completely to the cause he believed in. He devoted his best years and even life to the Chinese revolution and to the tough days and nights in the anti-Japanese base areas. He lived his life the way he wanted. He truly fulfilled his oath to the Party.