Deep Rock Galactic has crossed 500k sold copies a year ago, around new year. They have not given any further updates on sales as far as I remember, but 2019 was by far the most successful year so far, with most significant updates yet. There were also a few free weekends and numerable sales on steam alone. I wouldn't be surprised if we were close to 1 million copies by now and I'm sure GSG will let us know when that happens.
I won't go into maths as the price of the game has increased last year, and I'm sure a large number of players got it during a sale. Then there's also the supporter edition that helps GSG financially as well as purchasable soundtrack. As long as the devs keep up the pace they will be fine as far as money goes and with full release in few months I'm sure advertising for the game will increase significantly too.