The cat may survive short episodes of overheat, but I don't think it's good to run it that way for a long time. Here's a couple of things you could do. Read your computer for error codes (I'm not sure how it's done on an S600). Check the engine wiring hardness for evidence of brittle insulation. If it is brittle, you wouldn't be wasting your money buying a replacement harness, regardless of whether it solves your immediate problem.
There is a way to check for a clogged cat. It involves removing an O2 sensor and checking the pressure. I forget what pressures you look for (2 psi max?)
You may want to replace the check engine light bulb.
95 E320 Cabriolet, 131K