3 million sounds a bit much. I'd estimate an accurate figure would be 1/10 of that. The super-wealthy did leave for the country and students are remote learning, so many will have given up on their expensive apartments. But no one I know has left. Not in the last year anyway. I think most people who leave NYC leave because it's too expensive. People had started leaving before Covid began. Everyone in the US that wants a vaccine should be able to get one by the summer. I have no doubt NYC will be back to a million tourists a week again before long.