The greatest danger is probably at initial sudden power up of the high voltage dc input supply rail.
Gate drain capacitance can be enough to pop the gate insulation if the gate is initially left floating.
Whatever drives the gate may clamp the gate voltage, or it may not, and you cannot rely on the gate driver circuit being initially fully powered up before high dc voltage hits the drain.
Sometimes a gate source resistor is used, sometimes a zener, and sometimes the design of the driver itself clamps the gate to the driver supply and its usually large bypass capacitor.
In this circuit, I see nothing besides the zener capable of protecting the gate, so removing it may not be a good idea, unless you can protect the gate some other way.