Well, at my last check we had a bit of a play with the 'Sioux City' scenario.
Interestingly the aircraft was remarkably flyable with thrust only. Dependant on weight we had an N1 thrust setting (setting the N1 mode helps a little with the Ecam engine indications) of about 'datum 45%'. Applying thrust brought the nose up and decreasing, obviously, dropped the nose. Speed control was attainable using this and turns were achieved using differential thrust.
To sum the whole thing up, as a team, we managed to get the aircraft back to the airfield and achieved a landing, albeit some what 'heavy' but certainly walk away from.
Can it happen? Well anything can happen and an aircraft had a double hydraulic failure during takeoff due to a failure of one system and an overheat of the second system by the PTU. All it needs then is a leak in the third and you are in big trouble!
Enjoy