The general rule (barring any complex emergency) is that if you can takeoff on a runway in a jet, you can land back there.
The next generalization is that a 'standard' engine failure in a twin is considered a Land ASAP failure. That is, it is preferable to land as soon as possible overweight, rather than delay the landing for procedures such as fuel jettison (fuel jettison rates are around 2-3 tonnes per minute, so a 50-60 tonne jettison delays landing by 20-30 minutes). Additionally, most modern jettison systems are set and forget (almost). You set the final weight and the jettison occurs automatically until you reach that weight.
Jettison is normally only used when there is a flight time to the nearest airport in excess of the jettison time, or in the case of a technical (non emergency) problem (eg gear/ flap fails to retract on takeoff).
So, knowing nothing of the problem the crew were experiencing, I would say that at the very least it was an extremely odd decision to jettison fuel in the manner and location that has been reported. Will be very interested to read the report.