Hi,
OK so... rather than hand the plane back to the pilot, you want the computer to keep flying the plane but to not even try to respond to inputs, just freeze itself at the last setting.
I'm REAL glad you don't design autopilots for a living.
As I asked the last guy... Did you even think that comment through before you made it?
The pilot can disengage the autopilot when he want ... at least he is warned of something wrong instead a brutal disconnection.