I have _not_ faced such a situation before. However I would most certainly **not** continue to do any work for this place. I would leave the client in the mess, since they believe this person is literally a messiah; Let them Crash and Burn and not work on the systems when they're totally in IT fire, disregarding their pleas for coming back
Ignorance on such a level of misjudged character, by management, needs to be punished.