No power from shore power, genset or batteries would indicate that the main 12 volt Fuse in the 12 volt power distribution panel has failed.
In order for the 120 volt system to prevent 12 volts DC to fail would be the converter or inverter/charger. This should have no effect on batteries supplying 12 volts DC.
Only place they are common is in the 12 volt DC power distribution panel.
Salesman switch would only disconnect the batteries.
Look adjacent to the 120 volt circuit breakers for a small metal plate that covers the fuses.