teropa,your comment about the option to not use the FMC for descent and lateral navigation would be the safest and therefore the most likely to achieve a safe landing in the scenario in your original question.
I have to agree with tunneler re the engine failure. What you have experienced was definitely a malfunction but IMHO, not dire.
If you have doubt about idling jet, or piston engines producing thrust, let me assure you, they do. On the 757 we use RB211 engines and we line pilots call it the “racing snake” because it won’t slow down. If we’re ferrying an A/C we have to use speedbrake on the G/S to stop it accelerating. Only when we get Flap 30 does the A/C stop trying to run away with you.
I have only had one real engine failure when I was instructing. The windmilling engine was ok, but then that prop stopped turning and the drag increase was alarming. I’m rather pleased I was doing some stalling exercises with a student so we had lots of altitude to play with.
As an aside all of the 757/767 fleet (I believe) only has the pushbutton type autopilots. In fact the only time I have ever come across the paddle type, was when we had an old Monarch 757 on loan and that has since vanished. All you have to do to engage an autopilot is push the paddle up.