Maria Nikolaevna passed away on 17 July 1918, a month after her family was executed. She was 19 years old. She and her siblings were initially placed under house arrest by the Bolsheviks, but were eventually executed in a basement of the Ipatiev House. Their bodies were thrown into a mineshaft and later buried.
The Enigmatic Life of Grand Duchess Maria Nikolaevna: Unraveling the Secrets of a Russian Princess