I find this all a little confusing being as one of the Cirrus aircraft we maintain has a basic six pack in front tof the pilot and one Avadine screen, on that aircraft you have no choice but to fly in basic HSI mode albeit with a big map on the screen to the right of the primary instruments.
Fair point the G1 (Generation 1) had a 6 pack, not sure when they stopped producing these but guessing around 2003 so the vast majority of fleet have all glass either Avidyne fit or Garmin Perspective and 4 back up instruments, ASI, AI, Altimeter and compass.
These would not allow you to fly an ILS.
If the PFD failed and or MFD failed you can fly an ILS from the info on the GNS430's, both of which are independent.