A widower since 1921, whose only child, a son, had died young, Muck spent his last years at the Stuttgart home of Baroness von Scholley, the daughter of one of his oldest friends and fellow internee, who had been German Consul General in New York. Partially paralyzed from nicotine poisoning and immersing himself in Oriental philosophy, he rarely left the house during the last three years of his life. Muck died in Stuttgart, Germany on March 3, 1940. He was 80. Upon receipt of the news of his death, the BSO interrupted a rehearsal to stand in tribute to his memory. Geraldine Farrar wrote a letter to the "New York Times" recalling that she sang with him and the Boston Symphony on the night when Muck was "bitterly and unjustly assailed" for not playing the National Anthem and adding: "As your editorial correctly reports, he knew nothing of the request." She continued: "The fortunes of war brought Dr. Muck — as well as other aliens — no disgrace in an internment camp. I saw Dr. Muck several times in later years and I know he counted the years with the Boston Symphony Orchestra among the happiest and most fruitful of his career."