(a) as modes degrade does the aircraft get to the point of having nil computer assistance ?
Actually, if you go by the anti-bus crowd around here, the modes degrade as you
add FC computers.
With only one secondary FCC (of possible 5 total FC computers) available to connect SS/rudder inputs to the flight control surfaces you have a 727.
With either no computers, or no electrical power, you have mechanical control, thru hydraulic actuators, of the THS using the trim wheel, and the rudder using the pedals. Though set up to provide control while resetting computers, as others have said, you can actually land the aircraft, if necessary, in this condition.
Complete electrical failure, you've got no choice but to land it this way. Challenging and satisfying.
It is never divergent around any axis, regardless of the level of computer assistance or lack of.
The wonderful world of FBW.