In order to install steam I had to:
sudo dpkg --add-architecture i386
apt-get update

and then

apt-get install libgl1-nvidia-glx:i386


Steam installed without any issues, but after the next reboot a couple problems:
- There is no internet connection anymore.
- LightDM stopped working.

I am almost certain that I messed up the the architecture i386 or the libgl1-nvidia-glx:i386 install.
Any way I can restore the system from here? Especially without being able to apt-get without net?