There is cause for optimism in the numbers out of South Korea and China. Even assuming China has lied about their numbers (population ratios with Italy and South Korea vs China make that plainly clear, they lied to a large degree on the numbers), if China has managed to bring it under control through their extreme quarantine measures, then we can prevent it from killing tens of millions. South Korea seems to have considerably slowed it there. Japan has done a good job of limiting its spread.
China has 1.4 billion people, and they've had ~3,000 deaths (let's assume it's several times higher in reality). But we'll see tens of millions dead globally? No we will not. If you killed every person that has been infected in China, and extrapolated that event globally, we would not see tens of millions dead. So that premise is absurd, to an extreme.
I consider this to be a very serious situation, however, it's not very serious as a great mass mortality threat (unless it mutates and becomes far more deadly and we prove unable to slow it down or vaccinate against it). It's a serious threat for massive disruption to our daily lives, including severely harming the global economy. It's a serious threat to swamping our healthcare systems due to ICU demands and diverting our resources to managing the ongoing crisis (instead of routine, normal productive work).
Assuming this isn't going to burn out come Spring & Summer, the next step is to rush to vaccine, at any cost. That will end this thing globally. Maybe we'll need to vaccinate against it annually, maybe it won't come back after this year, who knows of course.
Tens of millions will not die. Tens of thousands might die in the plausible worst case scenario, before we get a vaccine ready. We can rush to vaccine at greater patient risk and financial cost, as necessary.