Better change the rear oxygen sensor with that catalytic converter. If the converter is bad, then the engine has been run with a misfire on that side.

As far as the torque converter, the thing that damages transmissions is heat. Nothing in a transmission is designed to wear out. What does it is transmission fluid begins breaking down around 180 degrees, and the manufacturer decided to 'cool' it off in the radiator, where the temperatures remain over 200 degrees. This deteriorates the hydraulic properties of the transmission fluid, and overheats the transmission. What locks and unlocks the torque converter is an electric solenoid, and just like the solenoid on most starters, they begin sticking when they are overheated, from expansion caused by heat. If left to, this sticking solenoid will either stop working altogether, or damage the component is is supposed to actuate. So, just keep in mind that torque converter USUALLY means whole transmission...

Secondary AIR pumps wear out, too. Infact, that might be what burned up the catalytic converter. This system is supposed to pump fresh air into the exhaust system to help lower emmissions caused by unburned fuel (which the catalytic turns into water). If it is malfunctioning, then the catalytic won't be able to keep up with the gas being pumped into the exhaust system. It will clog up, and little mini explosions will literally blow the catalyst into pieces, damaging the catalytic converter.

I hope this helps if you still need clarification, just let me know.