Deaths are currently running at about 1000 per day. That is from CDC data that is listed in Wikipedia.
Right now that 1000 per day is slowly declining. I personally expect that trend to continue but I see no reason why it will decline to zero very soon. Most bugs like this one essentially die out over a few years due to the natural herd immunity. The virus just runs out of infectsble victims.
But the current 1000 a day is 365,000 per year if it doesn’t continue to fall. And it will nail people in 2021, 2022 and perhaps further in the future.
So the 200,000 to 400,000 is just an educated guess. I hope I’m wrong.
I hope you realize most of those deaths aren’t actually from the virus.