I guess it depends on the car you are referring to. Every trans made byt a different manufacturer has a different torque converter set-up. TCC - Torque Converter Clutch
If your car has "lock-up" the friction plate inside wears out usually due to low trans fluid, burnt trans fluid from poor maintence, or a sticking torque converter clutch apply solenoid in the transmission valve body which causes the plate inside the torque converter to slip burning it up.
Now if you don't have tcc lock-up, then there basically is nothing to wear out inside the torque converter, except maybe a roller clutch.
When they are rebuilt they are cut in half at the seam, cleaned, friction disc and the pressure plate are replaced, along with the roller clutch if it has one. Then welded back together and balanced.
Does that help at all?
The torque converter should last the life on the trans, and should not be reused, unless rebuilt, in the event of a catastrophic trans failure. IE: metal hard parts fried inside trans.
Torque converters mostly only cause problems with the TCC apply, which cause a small vibration. If the friction disc is shot, you will get a shudder on TCC apply, and on slight acceleration at highway speeds.