Unless that has changed since the airplane was designed in the early 80's, the pilot should be able to regain control despite the electronics going berserk. Hydraulic power is required to fly, but not electronics.
Source: I worked on 757 flight controls back around 1980.
For the sake of discussion: Now suppose IFR conditions and a hypothetical directed RF attack vector which spoofs instrument nav/pos data...I'm thinking GPS, VOR, radar altimeter.
I'm not a pilot, but if I was "in the soup" when this happens, first I'd try radioing the ATC and asking Victor for a Vector out of it. Then fly that vector straight & level. No radio, then it's old-fashioned map, compass, and dead reckoning. A 757 has a lot of range, so you should be fine.
My father was a navigator in B-17s, and used celestial navigation. I suppose they don't teach pilots that anymore.
They do, but you need to be able to see your references to be able to do that.
Edit: also some aircraft are going totally glass. I've seen some homebuilts and super cubs without steam gauges completely, and it's just a matter of time until Cessna, Boeing, Airbus, etc eliminate them.
That's what I said upthread a couple of posts. The penlight thing was in response to someone saying what to do if it is too dark to read the instruments.