I have a 2000 ML320 (original owner!) with 155,000 miles. Left for skiing road trip. After an hour, "check engine" light comes on. Stopped at MB dealer. Says catalytic converter needs to be replaced ($1300 + $300 labor). Asked if OK to drive rest of trip (250 miles) and repair next week. He says yes. Drive another hundred miles, and check engine light comes on... then loss of power. Pulled over. Turned off engine, waited five minutes, then restarted. Drove about a mile then same issue. Turned around and tried to drive back. Made it three miles and car gave up.

1 - What are chances I have permanently damaged engine?
2 - If I replace cat, will I likely be OK?
3 - Anyone had success using non-OEM parts such as from eBay?

I am, of course, in the middle of nowhere in a town of 14,000 people (better than being on side of road, I guess). Thank you for your advice.

 

99% there is no damage to your engine.
75% your exhaust is clogged do to broken convertor inside of it's housing.
If you are not in the state of Ca., aftermarket exhaust or one of the convertors should do the job. Have someone check the exhaust back pressure.