There are two arguments hidden in this discussion:
One is the decision the crew made. There are always different points of views in such cases. We can safely argue that most pilots wouldn't return inflight based solely on status messages. All options have to be weighted, inclusive the weather and traffic situation in Moscow.
The other point is the system itself. For me it's amazing that you can loose such a big portion of an engine without loosing thrust, or even having no warnings. They lost basically most of their duct wall and outer cowling, still there is no sign of it in the cockpit? Eighter 777 are wonderfull aircraft... - or the opposite. Wouldn't there be a massive deterioriation of aerodynamics inside the fan duct? I can hardly believe that all this honeycomb material went through the fan or through the outside without causing damage on the engine itself.
And if you loose a whole chunk of your reverser, doesn't that trigger any warning on the flight deck? I'm really astonished.
How big is the increase in fuel flow? No temperature deviation?
And on a 5 hours flight over sparsely populated area, wouldn't there be time to stand up from your "armchair" and have a look on your troubled engine? I guess the feedback to maintenance would be very much different than based on status messages, and so would be the answer from MCC.
So, all in all, I tend to be in the group of "there was something wrong" in this incident. But more information would be necessary to get a definite picture.