What would cause rear defrost switch and heater switch to quite working on a 1992 geo metro no fuses are blowing?

Are you talking about two separate switches?

The rear defrost switch might have corroded contacts or a bad spring mechanism. The factory manual recommends you pull off a few covers and drop the steering column to get to the defrost switch, but I found that some careful prying at the top and bottom of the defrost switch where it meets the dash with a knife point or thin flat screwdriver will get it to pop out. If you are adventuresome, pop the switch open and clean the contacts (look out for a flying spring!) , otherwise get one from the dealership or friendly local junk yard.