Never had a need to know....until now.
Opinion | What You Should Know Before You Need a Ventilator - The New York Times
Other articles indicate chances of survival vary based on how ill the patient....50-65%.
Add to this sad situation the fact family will not have been in contact (except by phone) with a loved one before needing to go on a ventilator with COVID-19....and not able to communicate once on the ventilator.
Maybe if more people knew more about ventilators they might become fearful enough to abide by the guidelines to prevent the virus and stay home.