a1rm4n and Volume, I don't think you appreciate just how big a deal even 1% fuel burn is on a big, long range airplane such as the 777. 1% fuel burn is a ton or more of fuel
per flight (depending of course on the flight length, but remember the 777 is designed to be a long-range airplane). That is a whole lot of fuel over the 20+ year life of a 777. And even if it adds 1,000 lb. to the aircraft empty weight (it won't), it'll still be able to carry 1,000 extra lbs. payload per flight since it won't need to takeoff with that fuel.
As for complexity, hydraulically actuated movable surfaces are a feature on nearly every commercial jetliner ever built, and they've been hugely reliable.
The original 777 folding wing concept was well inboard of what's being used for the 777X and far more complex. Among other things, there were various movable aerodynamic surfaces outboard of the fold - not so with the 777X. In the highly unlikely event that the folding wingtip fails in-flight, it's only a couple percent of the total wing area and the aircraft will fly just fine (although I'm sure there will be plenty of "I thought we were going to die" stories in the news afterwards
.) As for not having a gate if the wings fail to fold after landing, I seem to remember something most airports have on hand called "air stairs". And as Saddler and CCA have pointed out, if the airport doesn't have a gate that can handle a 777X if the wings fail to fold, they couldn't handle the 777X if the wings weren't designed to fold.