You can disable a servo channel output on the Maestro by sending a set target command with a target of 0. When the Tic loses the signal, it will trigger the “Required input invalid” command, which you can configure to behave in a few different ways, including de-energizing the stepper motor. Alternatively, you could set it to “halt and hold” or “decelerate to hold”, and set a much lower current limit for it to use during the soft error. All of this can be configured in the “Advanced settings” tab of the Tic Control Center.
Alternatively, you could configure a separate channel on the Maestro as an output and connect it to one of the pins on the Tic that you configure as a kill switch. This will also trigger the configured soft error response.