1996 Toyota Camry Catalytic converter

I am told Toyta Camry has two catalytic converters. Front at Exhahust manifold and rear at the bottom. About 3 years ago my mechanic discarded the rear converter saying that the car would run fine with the Front converter. The car passed the emission and had since been driving fine. For the last couple of years i have engine chieck light coming on and off. Now for serveral months it is constantly on. The car has been running fiine with no apparent problem. About a year ago I took the car to a mechanic to check the car for the Engine Light. He checked with some handy computer ( perhaps for some codes) and told me that I need to replace the catalytic converter. I just need a second opinion about this issue. I am not sure if I need to replace the Front Catalytic converter only or I have to install the second or rear Catalytic Conveter also in addition to the Front conveter. I am not sure if the Enigine Check light is really about the Catalytic Converter or it indicates any other malfunction. My Emission Inspection is due this month. If it fails the Emissions test, would the inspector able to tell me if the car needs a new catalytic converter of something else. I would certainly make a donation if I could be educated about this problem. Please tell me if i need to replace oxygen sensor also with the catalytic converter.

Thanks
Inam Haq