"IF" is a mighty big word Mr Dog!!! So let me get this straight, the Captain was in compliance with FARs and the flight turned out just fine!
The reason quads have 4 engines is to improve safety if one stops. 747ER weighs 910k and has 252k thrust, a 330 weighs 510k and has 160k thrust.
He was in a slightly worse position thrustwise but in a much better position in terms of redundancy than the average twin embarking on a 180 minute ETOPS sector at high AUW. If you lose another, your Thrust to Weight on 2 differs from the twin on 1 by <10% at MUW.
Maybe all twins shoul be converted to Tris or maybe we should get all the B52s out of Davis so that we can debate 5 engines failing on an 8 engined aircraft. Following the so called experts logic above, reversion to 7 engines would require an immediate diversion