I am not an expert on this subject. I think if you do a search you can find some info. I know there are 3 or 4 brands of after market Cats available and they are a lot cheaper than the OEM. I believe the danger of letting it go is it could clog up and/or over heat as the guts fall apart. Or it might just make noise. Some of the aftermarket ones are not that expensive. It depends on the car. Hopefully someone can recommend one for you to buy if you choose to go that way.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra