By the end of 1973, those closest to Warner became aware of signs that he was becoming disoriented. Shortly after losing his way in the building that housed his office, Warner retired. In 1974, Warner suffered a stroke that left him blind and enfeebled. During the next several years, he gradually lost the ability to speak, and became unresponsive to friends and relatives. Finally, on August 13, 1978, Warner was admitted to Cedars-Sinai Hospital, where he died of a heart inflammation ("edema") on September 9. He was 86 years old. A funeral service was held at the Wilshire Boulevard Temple, the synagogue to which many members of the Warner family belonged. He was interred at Home of Peace Cemetery in East Los Angeles, California.