1992 toyota camry

I believe that oxygen sensors, like spark plugs, are wear items and should be replaced 100-120K miles. Personally don't know anyone needing to replace a converter, the most common of which contain platinum coated substrates. On older cars burning oil (from leaking piston rings or valve stem seals), leaking coolant past head gasket, faulty injectors and such can contribute to converter and oxygen sensor failures.

Sensors can go bad without setting MIL code and as a result damage the catalytic converter. But before replacing the converter or sensors, you need to make sure the car is tuned up (timing, spark, valve gap, etc), has no false air entry before the sensors (holes in pipes or leaking gasket, etc), and then suspect the sensors before you suspect the converters.

The newer Camrys (post 97) using heated Denso sensors are having problems with bad catalytic converters, sulfur smells and poor mileage. According to TSBs Toyota has had a lot of problems and has to reprogram the ECM or replace converters and such. And having solved a P0420 using all new Bosch planar type sensors (upstream and downstream), I came to believe Denso sensors suck. Glad I didn't recommend to the owner a converter replacement in that case.

See: Bosch planar type (more resistant to contamination because of the design)

I'd begin by checking that the car is working properly (not burning oil, leaking coolant past head gasket), properly tuned up, then checking for false air, and then suspecting the sensors. Unless the converter substrates had fallen apart and shaking loose inside the P0420 may be a problem elsewhere.

You do have to fix the cause (and not just slap a new converter on the car unless it's really the converter) or the code will come back again down the road.