Question...
Question: When the LCD PFD fails (one or both depending on the aircraft), what do you back it up with? Answer: A backup artifical horizon, airspeed indicator, and heading indicator.
Question: When the GPS unit (or screen) fails, what do you back it up with, when you're using it for primary navigation in IMC conditions? Answer: It seems to me you'd back it up with VOR, DME, and ADF (along with radar directed ATC when it's available).
Why lose the ADF when it might be needed? Comments are welcome.