The Check Engine light came on in my 1999 4Runner and I took it to the Service department at the dealership. They called to inform me that the problem was the catalytic converter and it would need to be replaced--for $1500. I decided to try and have my neighborhood mechanic do the work instead for much less. When I called him for an estimate, I mentioned that the Check Engine light had not come on since I picked up the car, which had been 3 days prior. He said to wait until it did, then bring the car in and he could do the work for $900. As of the the Check Engine light is still off and it has now been three weeks. Was the original trouble a fluke and I don't need repair? I'm worried because I have long car trip coming up and I don't want to break down.

If the CEL has not come back, i would not worry about it.
The OBDII system is not perfect, and can generate false codes.

Even if you had a code for a bad cat converter, the odds are that it is the HO2 Sensor 2 which is at fault and not the cat converter. The ECM determines the quality of the cat converter by monitoring it with the HO2 sensor after the cat converter.