You've all danced around it - but missed the real issue..... The 212 had a single thread AFCS. If that one system failed, you had nothing but the basic handling qualities of the airframe. The basic airframe did not provide sufficient inherent lateral stability to meet IFR handling requirements. Hence the big fin on the roof (It's for lateral stability - not yaw).
In the 412 the fin went away because they went to a redundant AFCS. Most other newer IFR machines out there have redundant systems - dual or better - so that a single failure still leaves you with SAS capability. You still have to have reasonable handling after a dual failure to "white knuckle" fly for 30 minutes. But the workload is allowed to be higher since it takes two failures to get there.
If the stability after a dual failure is not good enough, the Authorities drive you to a 3rd level of SAS. For example, I understand the EC-135 has a "limp home" SAS capability using some extra pitch and roll rate sensors that are plumbed into the actuators when both FCCs fail. It's not fully triplex (since it uses the same actuators) but it's close.
Hope that helps.
Avnx EO