Well, on the classic, the engine spins to prevent over-reving MG1, which would happen at 42MPH if ICE did not spin.
On the 2G, the rev limit is 10K, not 6.5K, so the car could be going faster before ICE would have to spin to prevent MG1 damage.
Yes, the drive belt does drive the mechanical water pump, but if ICE isn't fired, the coolant doesn't need to circulate, as there is no excess waste heat to get rid of. If you need cabin heat, there is an electric pump to provide circulation for the heater core.