This affects our game 2 machine (176.57.141.141) and all gameservers running on it. Seems like the system upgrade I did today didn't work out so well (even tho it exited with a success), and performing a "reboot" causes the server to not fully start up again - suspecting a kernel panic of some sort. Adding insult to injury, the web interface for controlling the server is broken as well, so I can't even start a rescue system / do a reboot (and apparently, start a reinstall either). Thus, I have opened a support ticket and am now waiting for them to answer, which, in the worst case, can take up to 24 hours. Will update this thread if there is anything new.
Same happened to my brother's server and then we decided to quit because we couldn't figure it out and the old version messed up somehow as well so.. Best of luck with this!
Update: Decided to start a full reinstall of the machine. While the rescue system finally booted, it is running an ancient version of Debian (3.1, EOL'd in 2008), thus the entire software raid stuff didn't want to work properly (not mountable). Clicked the button about 4 hours ago (as of this post), state is still "installing" and the server itself pingable.. Contacted support AGAIN, not sure if anything will happen anymore today (how hard can it be to change the boot order?) Meanwhile, I have confirmed that our backups are indeed working, so once the OS is installed everything should come back pretty fast - given the backup server can sustain 1 Gbit/s outgoing traffic (backup size ~91GB).
Update: Turns out that both of the currently installed HDDs are too old (lol) for the OS I wanted to install (latest Debian stable). The only option there would be to install an older OS, which doesn't really make sense (and isn't really secure either). Therefore, both HDDs will be switched out for a SSD tomorrow morning/afternoon, and the OS installed on it. On another note, the thing which connects to the server's reset button was broken as well, which would explain the server not wanting to restart at all. It has been replaced now as well.