If you havn't 400V NPN transistor for using in 325V net, is it acceptable use 1kV diode in series to NPN transistor (150V) collector? This is low current part of circut so additional losses is not important.
VT2 is used to increase Hfe of VT1 but has low Vceo. In case VO3.2 is closed VT2 is open and collector-emitter voltage less than 1V because almost all voltage will be on load. In other case closed VT2 will be burn by high voltage. So my question is will additional diode before VT2 collector protect VT2 from high voltage?