I spent a few hours on this yesterday trying to replace the VOM1271's which are very hard to come by (and also bloody expensive).
When a non-isolated gate voltage is used a zener has to protect the high fets gate from being pulled too low. Now when Vgs goes positive it tries to flow through it so a reverse diode is needed (D1, D2).
The fetDC goes up to ~18V but in AC over-voltage the gate can now be 100v - zener, D7 prevents backflow now as Q5 can't handle > 7V.
By introducing D7 the transistor to ground (not shown on diagram but was under Q5) can't drain the gate. Therefore R5 must be lowered into an acceptable range.
At 100v - zener there's quite a flow through a low value R5.
And I'm in a loop!
So isolated drivers are definitely the way to go, I just don't want to rely on an almost impossible to source chip to make it work.