@ JT,
From what I have read about the A330/340, IMHO, both possess static and dynamic stability to the point that in the worst situations, the aircraft is flyable. If it were not, I don't see how it could of been certified in the first place. I think the Airbus folks, designers, engineers, aerodynamicists and software folks thought of virtually everything to enable this, complicated as it may seem or be.
The worst two cases would be Direct Law and/or complete loss of electrical power.
Direct Law - In pitch direct law, elevator deflection is proportional to stick deflection and, in all configurations, max elevator deflection is a function of CG. This should be a transitory phase prior to PRIM reset and re-acquisition of Alternate Law. There is NO automatic trim meaning you have to use manual pitch trim. The yaw damper still provides yaw damping but gives minimal turn co-ordination. So protections of g, pitch attitude (manual pitch trim is required), high alpha, high speed, bank, MLA, turbulence, low energy and AP are all lost. But, the aircraft is flyable with care.
Should a complete electrical failure occur, mechanical pitch control is through the THS using the trim wheel. There should be caution here as if the CG is back there is a pitch up bias, if the CG is forward there is a pitch down bias. Manually operating the trim wheel requires gentle and smooth movement as the THS is a large aerodynamic surface. Mechanical lateral control is the secondary effect of rudder pedal inputs. The BYDU provides Dutch roll damping.
An example of an event which would put you in Direct Law would be a double engine failure, which at high altitude cruise, would probably mean that you will need to descend in a controlled manner to a lower altitude to initiate engine restarts.
I would say a good example of a unstable large aircraft without FBW computer controls would be the B2 USAF bomber. If the computers quit, IMHO, the aircraft would not be hand flyable.
Just some thoughts and opinions from a non-pilot, engineering type.