Okay, thanks but I think the Schottky alone would also not help if the voltage was 12 V; it would just deliver that to VCC and break the MCU anyway? I could understand if the argument was that the zener and Shottky could work together. I'm not actualy expecting the MCU to be off when the MOSFET drain is high because the 12 V will also be going to the voltage regulator for the MCU. A broken connection or damaged regulator could do it.
I understand. Thanks.