I just bought a second 190E 2.3-16, Euro model, that has had a cat failure. On my first one, I owned the car until I gave it to my son recently. The cat failed on that car because the pipes coming to it rusted and the casing itself corroded away in 15 years of daily use in the Northeast. I replaced it with an aftermarket unit that fit just fine, and has worked for another 3 or so years. The car has 216,000 miles now.
The second car has 120,000 miles and is on its third cat now. The first replacement occured in 1992, so I don't feel too much like I am heading in the direction of your experience. Yet. But your tale makes me nervous. In the second car when the cat went my wife was driving it and she drove it until the car would not move. It would start and idle but not rev past 2,000 rpm. The car runs fine now with the new cat installed, and it has been running fine for about 1,000 miles.
I can't really offer a solution but am very interested in the way your problem works out. Please keep us informed on how this saga pans out for you, if you don't mind. Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)