In 742, Niu was gravely ill. His former assistant at Shuofang, Yao Hong (), a grandson of the deceased chancellor Yao Chong, had been favored by him due to Yao Hong's dabbling in supernatural matters and claimed to know how to avoid misfortune. He recommended Yao to serve as imperial censor. Now that he was ill, he asked Yao to pray for him—and Yao did so but forced Niu to recommend Yao's uncle Yao Yi () and the official Lu Huan () to replace Niu himself as chancellor. Yao Hong went as far as writing out the petition and forcing Niu to sign, but Niu was so ill that he was unable to sign properly. Niu died in fall 742. After his death, his wife, when imperial messengers came to mourn him, showed the imperial messengers a petition to accuse Yao Hong of extortion. In anger, Xuanzong forced Yao Hong to commit suicide and demoted Yao Yi and Lu. He awarded Niu posthumous honors.