When you have a bad catalytic converter you can drive the vehicle with the bad catalytic converter for as long as the vehicle will run.
If the catalytic converter gets too bad then it could cause your engine to stall, rough idling, loss of engine power, hard starting.
If your catalytic converter is bad you may also fail emissions testing and also have increased fuel consumption.
Sometimes a catalytic converter may just be slightly clogged and need cleaned using some catalytic converter cleaner that you pour into your gasoline tank when full.
The catalytic converter cleaner when burned in the combustion chamber along with the gasoline helps to clean carbon deposits from the exhaust system and catalytic converter.
If your state has emissions testing then you will have to replace the bad catalytic converter with a new one if the car is worth it.
Or if your state has no emissions testing then can have the catalytic converter removed and go without the catalytic converter.