Whatever happens, be sure to post the result to help others in the future.

If you have easy access to other cars that run / all parts from the same car, get the engine computer / DAS X box behind instrument cluster ( clipped above the brake peddle box black 3" x 5" X 1", should be marked 210 820 32 26 ) and key.

Pop the antenna ring out of the dash ( around the ig lock ) or use the antenna ring from the parts car. Swap both boxes, put the key that goes with the boxes in the antenna ring, use tape or something to keep it from falling out. Make sure that antenna ring is plugged in to the dash box and kept away from the key that turns the lock. Use the original key to turn the ignition lock / start car.

A computer from a 97 SL320 / C280 will start and run the car. The C280 will run the car but it will lack power / bog, not sure if it will relearn I didn't drive this combo very far. 97 S320 would also work , 98 / 99 might work as the motors are the same. 98 up V6 cars won't work.

Does the original key fob look like it fell apart? There is an RFID chip inside that is read by the DAS X box, if this is missing the car won't start. In this case, you can get a flat key from the dealer that has a chip and it will start the car _IF_ the original computers are OK.