CD Projekt has looked back on the first half of 2019 and has commented on their sales and revenue makers, The Witcher 3 is still a main means of income for them.
CD Projekt RED has released a press release detailing their revenue for the first half of 2019 and it reveals that The Witcher 3 sales still "remain strong". The email excerpt which has been provided by Dom on his personal Twitter page quotes Piotr Nielubowicz: "In the first half of 2019 gamers actually purchased more copies of The Witcher 3 than during the first of the previous year!"
If I was to give a guess as to why The Witcher 3 sales are still going strong and are actually improving, I would say it would have something to do with Netflix's Witcher TV show that is expected to launch by the end of the year. Perhaps fans of Henry Cavill (actor who is playing Geralt in the TV show), enticed some new gamers to give The Witcher 3 a shot before both the show releases.
While I know that the upcoming TV show isn't based on the video games at all, I believe that buying a game and stepping into its world is much more easier feat than sitting down and reading lengthy books, as good as they may be. For this reason I believe that the announcement of the TV show certainly influenced - to some degree - the 2019 sales of The Witcher 3.