Short answers, pulled from the story.
Vladimir Lenin died at 18:50 on the 21st of January 1924, at Gorki, at the age of 53. Soviet authorities recorded the official cause of death as an incurable disease of the blood vessels.
Trotsky was convalescing in the Caucasus at the time of the funeral and later claimed he had been given the wrong date for the ceremony. Stalin's personal secretary Boris Bazhanov corroborated this, stating that Stalin sent Trotsky a telegram with a false date for the funeral. French historian Pierre Broue also cited Moscow archives showing correspondence between Stalin and Nestor Lakoba, secretary of the Abkhazian party, as evidence of a deliberate effort to keep Trotsky in Sukhumi.
Mikhail Kalinin, Grigory Zinoviev, and Joseph Stalin each delivered speeches at Lenin's state funeral on Red Square on the 27th of January 1924. Leon Trotsky was notably absent from the ceremony.
The Soviet leadership ordered Lenin's body embalmed for permanent public display in the mausoleum on Red Square, overruling the explicit objections of Lenin's widow Nadezhda Krupskaya. The decision was made to allow long-term public viewing of the body.
Lenin's brain was removed during the embalming process. In 1925, an institute was established specifically to study and dissect it, and the examination found that Lenin had suffered from severe sclerosis.
In 2018, Russian MP Vladimir Petrov proposed that Lenin's body be buried in 2024, on the 100th anniversary of his death, arguing that housing the remains in the mausoleum was costing the state too much money. Petrov also suggested replacing the body with a wax or rubber model. The proposal was not carried out, and the body remained in the mausoleum as the centenary arrived.