Is “Angrily beheading the envoy and fighting to the death at Mianzhu” true?
attested in history
Records of the Three Kingdoms, Book of Shu, Biography of Zhuge Zhan records his refusal of Deng Ai's offer of a kingship, beheading the envoy, and dying with his son Zhuge Shang at Mianzhu; the novel Romance of the Three Kingdoms follows the official history exactly.
Zhuge Zhan
Both official history and the novel depict the killing of Deng Ai's envoy and the father-son sacrifice at Mianzhu.