Ginsburg Mega Post
Most states have their own laws regarding when someone is considered "legally dead." The Uniform Determination of Death Act (UDDA) is a model state law drafted in cooperation with the American Medical Association, the American Bar Association, and the President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research.
This is a model way to treat legal death and then states are free to accept it or change it. The act has since been adopted by most US states and is intended to provide a comprehensive and medically sound basis for determining death in all situations.
Ginsburg was treated in New York and presumably, that is the state we would need to confirm to the extent they follow the UDDA exactly or have state specific changes.
Apparently all 50 states in the US recognize that someone is legally dead once they are brain dead, meaning they have “sustained irreversible cessation of all functions of the entire brain, including the brain stem,” according to the Uniform Declaration of Death Act (UDDA). Sauce: https://qz.com/1253987/a-legal-quirk-means-you-can-be-dead-in-new-york-but-alive-in-new-jersey/
So if Ginsburg is brain dead in New York, she is legally dead. Irreversible cessation of ALL functions of the entire brain, including the brain stem.
Even a cursory review suggests brain cells can survive even after bodies "die." Sauce: https://www.livescience.com/27423-brain-cells-outlive-bodies.html
And if you own the Doctors making the medical determination if the patient is brain dead? Easy to keep someone "legally alive" way longer than they are not able to function.
For More In Depth Review See: https://www.health.ny.gov/regulations/task_force/reports_publications/docs/determination_of_death.pdf