On twin-engined aircraft the standard procedure for engine failure is to land as soon as possible. Since it is possible to land overweight—and aircraft are designed so that it is—delay to dump fuel is not considered acceptable, and no reasonable pilot would delay the landing when they can land already.
Landing overweight is not really a big issue. The limiting factor for maximum landing weight is the kinetic energy of the aircraft that will be dissipated on the brakes as heat. If the aircraft is overweight on landing, the brakes will probably overheat. But:
- Since they had engine fire, the fire engines were on stand-by anyway, they can deal with hot brakes too.
- The heat often causes tires to deflate and the brake pads might be burned, but those need to be replaced quite often anyway, so it's not a big loss.
- The aircraft can't depart again until the brakes cool down, but it's not flying anywhere until they replace the failed engine anyway.
So it's safer to just land overweight than spend longer in the air with only one engine.