I had in mind a DA42 as my example.
The backup instruments are the AI, magnetic compass and altimeter. The AI is electric. There are no other backup instruments and no other radio navigation aids. (Other than whats in your flight bag). There is no manual engine instrumentation, although of course there is manual rudder and elevator trim, flaps and gear (although flaps and gear are electric, but dont worry if you run the backup battery dry because with diesels both engines are going to stop at that point anyway).
Primary systems can be displayed on either panel in the event one fails.
As IO540 says (perhaps in the very unlikely event) both backlights failed all the G1000 systems would be worthless (because there would be nothing to see if they were working). I am still researching the consequence of full AHRS failure (effectively the central computer through which the majority of the avionics operate).
However unlikely it is, a dual panel failure is what provoked my interest.
I suspect the reality would be you would also be without the "on board" radios becasue even if these continued to operate you would have no way of knowing what frequency was selected (although I suppose you could stay on the last selected, or if really clever might work out how many turns did what!!!
).
Perhaps it was in the mind of the designers that the backup instruments are only there to deal with selective failure of individual G1000 units (which after all is modular) - for example the loss of the glass AI.
Alternatively maybe it was in their minds you could survive on just the backup instruments which is what provoked my question. If that was so it might be odd that they did not also include a G/S perhaps - opinions please.
Of course I appreciate it is a cost versus risk scenario equation but for a "serious" IFR platform costing a very substantial sum a backup G/S is a very small percentage of the whole package.
(Personally I dont go any where without a GPS and radio in my bag - sorry if I fall into the pro GPS group, and as it happens I even put the liferaft in any twin I taking over water in spite of the ribing I always get).