Found this after digging around in AskUbuntu:
It's still possible to make the change from the command line using dpkg. Credit goes to this site: http://www.humans-enabled.com/2013/10/ubuntu-1310-enable-controlaltbackspace.html. To sum up what's written there, you can open a terminal and enter
This will take you through a series of options for the keyboard; for the first 4 or 5 just hit enter to keep things as is, and you'll end up with the option to enable Ctrl-Alt-Backspace.
$ sudo dpkg-reconfigure keyboard-configuration
This will take you through a series of options for the keyboard; for the first 4 or 5 just hit enter to keep things as is, and you'll end up with the option to enable Ctrl-Alt-Backspace.
