re: What percentage of Covid patients that go on ventilator get off the ventilator alive?

We're probably not going to be able to get this information in a real-time crisis setting. That said, I look to the number of deaths per day versus the number of positive cases as that is probably more telling of how much the ICU's are being impacted. That is, the vast majority of people testing positive have a slight fever and just go home. The deaths are indicative of people who were, almost certainly, in ICU prior to their deaths.