Hmmm… OK, so this gets very strange. Although the “workaround” I found worked for a while, now I’m in the same position - there is no longer anything in the /sys/class/backlight directory! My Pi is still running, but the touchscreen display is permanently OFF.
How can modifying a file result in the removal of the parent directory (and all it’s contents)?
The last thing I was doing was modifying the /home/pi/.config/lxsession/LXDE-pi/autostart in order to get chromium running fullscreen on startup.