Two comments on your post.
1. Pitch plus power equals performance. You set the power, maintain a pitch attitude in reference to the horizon and you keep flying. Maybe not at a perfect altitude or speed, but you stay in the air.
2. The old parable of the scorpion crossing the river on the back of a frog. If “the good guys” disable all the nav and flight info to the flight deck, then they defeat the hijcacker at their own peril. They might prevent a 9-11 flight into an innocent target, but they just sealed their own fate and those of the passengers.
I dont think it is possible to fly a 777 in the dark of night with a dead panel.
If you can't see the panel, I don't think it is possible to feel fly a heavy aircraft.