[jb92563]

The Cats are designed to last forever basically and this would be true it they never became fouled by oil in the exhaust over a long period of time, excessive temperature (overly rich unburnt fuel getting into exhaust) or mechanical failure of the converter element (rock smashed Cat or Internal cement came apart causing cat element to loose its seal and allowing exhaust to bypass the element).

I had a Cat failure at 75K miles due to the cat element cement losing its seal.
You can hear the element sliding back in forth inside if you shake the removed cat.

I replaced it with a used one from ebay since Dismantler Businesses are not allowed to sell them used in CA. Works better than the other banks cat now and cost ~$250 vs the ~$1800 for a new one.

I used a scope through the front O2 sensor after my AOS failure a few years ago, figuring that I had oil fouled the cats but it looks fine.