microcontroller output fail safe circuit
If you have another IO pin you can toggle at say 1kHz in your main loop in the processor, you can use it through a charge pump to store a charge on the gate of a MOSFET. The MOSFET should turn on when the clock is running and you can use the MOSFET to act as an additional switch in your LED drive or otherwise integrate it into the driver logic.

Some tuning of component sizes is required, MOSFET should have a low value threshold.







simulate this circuit &ndash; Schematic created using CircuitLab

Note: You could simply replace your current turn on circuit with this one and have the turn on function send out a suitable square wave instead of a DC level.