I can't change the password because the site is still down. Although my password is randomly generated and different to any of my others.
Update 2 days later: Yep, I'm one of the 31M affected users. Still waiting for the site to go up so I can change the password. Check if you've been affected on https://haveibeenpwned.com/
Yeah for sure. You can still download it from Steam at the moment if you already have a license for it, and probably for quite some years, so thank God for that. But if it ever stops being available for download for some reason from Steam, the game won't be able to be downloaded at all anymore. On GOG, as long as you kept a backup of your personal installer file, the game will always be installable forever as long as you don't lose your backups and there isn't some crazy post-apocalyptic event that takes away our technology.
The advantage and point of the DRM-Free nature of GOG is that once you download a game, it stays on your computer even if the game is removed and made unavailable to download. And you are able to download an "offline installer" file which can be backed up and used to install the game at any point in time even without an internet connection. So buying it on GOG knowing it may be removed is still hugely advantageous.
I checked GOG as soon as I saw this post. Hopefully they don't take that down, too.
[Goes and cries in a corner]