I think there are two separate discussions here. Firstly the apparent misbehaviour of an autopilot; as described, the AFCS system had failed and needs to be snagged. Indeed the failure mode appears to be 'fail un-safe' and is worthy of a formal report.
Turning to Nanny, on the DA62 you have a number of options regarding her including switching off the ESP. Like most light aircraft, the DA62 will happily let you crash spectacularly.
