They will last basically forever if you take care of it. If you have a problem, it's upstream or downstream, 99% of the time. You might have an exhaust leak. Unless you're caboning out the converter, or it's running way too lean, look elsewhere. the catalytic converter usually a symptom, not the cause. You might have accidentally knocked off a vacuum hose, O2 sensors could be off... 

The staff at AutoZone are not mechanics. Many barely know how to look parts up on their computer let alone diagnose anything. Did they tell you the actual code that came up on "their machine"? Probably something like a P0420 if they said it's a converter problem. There are several different things that the problem might be other than a catalytic converter such as an exhaust leak, bad O2 sensor, etc.

https://www.way.com/blog/p0420-code-what-it-is-and-how-to-fix-it/

You need to find a good local mechanic who will actually troubleshoot the problem. (Stay away from dealers as well as chains like Pep Boys, Firestone, and Midas.)

If your catalytic converter is actually bad, as long as it's not clogged up and not causing any other problems (check engine light stays solid, not blinking) you can keep driving the car. The issue would be the vehicle would not pass state inspection if you're in an area where that is required.

Well I've actually seen people drive them years that way. If the vehicle does not overheat on the temperature gauge and to can drive it normal speed 70 80 on the highway, you could drive it basically forever. Then. It's not a serious problem until the engine light starts flashing on and off as you drive

forever