Of the covid-19 patients who become so ill that they required a ventilator, what percentage of those patients actually recovered?

Relatively small %: New York City officials have stated that at least 80% of people placed on ventilators due to COVID 19 have died (& there are similar stats in other cities). REF: https://www.businessinsider.com/coronavirus-ventilators-some-doctors-try-reduce-use-new-york-death-rate-2020-4. In a British study ICU study 66.3% of mechanical vent. patients & 19.4% of basic respiratory support patients died.