So I had this long-running problem where as soon as I installed the drivers for an nVidia GPU, I'd lose the terminals (normally accessed by Ctrl-Alt-F1, Ctrl-Alt-F2, etc). The processes were still running, but nothing was visible. This was particularly annoying if I did anything to trash the desktop environment --- couldn't get access to a terminal to fix things.
Turns out the solution though is pretty simple: modify the file /etc/default/grub so that instead of saying "quiet splash" it says "nomodeset" (make a copy of your original grub file first to be safe):
#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"
Then run sudo update-grub. Upon reboot, the TTYs will be visible again. Spews out the entire boot log to the screen as well, but that wasn't really a concern at all for me.