Impossible.
In the hybrid, the electric traction motor is never "off." And except in one specific situation, it is the only thing propelling the car. It gets electric power from a combination of the ICE-driven generator and the battery.
The specific situation is speeds between about 45 and 75 mph, and low acceleration. Then the clutch engages, allowing the ICE to propel the car. The generator still spins, but is electrically disconnected. So it acts as a flywheel. The traction motor is still operating, and moderates the power sent to the wheels by acting either as a generator or a motor.
In maintenance mode, all that happens is that the car won't go into EV mode. The only potential problem is that any excess power needs to go somewhere. If the battery becomes full, the car should lower the power level of the ICE to prevent overcharging.
+++++
I have used Maintenance Mode in my HAH (which, incidentally, is not a PHEV, and never was in Gen X) before. You turn off off by turning the car off.