Melted Fuse Box

My 2000 Saturn wagon overheated, so I drove it to a repair shop. When they started the car, smoke immediately came out of the hood. When they opened the hood, they saw that the lid of the main fuse box had melted. The fuses were also melting. The repair man shut turned the key to turn off the car, but it kept running. He then disconnected the battery, but it still kept running. Finally, he unplugged the coil. What is this about, and is it worth fixing on a car with 120k miles?