It's obviously not good if one fails and the engine falls off the plane, but, a 777X should still be able to fly with a single engine.
Of course, that capability is more geared to "we saw a high temperature on the engine so let's proactively shut it down and land as soon as we can" and not "the engine fell off the plane and landed on someone".
It is a safe-life part, so yes, it is a single point of failure part for that engine. And, if something fails unexpectedly, it could significantly damage the wing too, as has happened in the past with deadly consequences.
The problem being encountered on two other test planes, makes it a lot more problematic, as the probability of the second engine shearing off then becomes a lot, lot higher.
Also, the engines are pretty close to the centre of mass so it's not a huge deal. Asymmetric thrust will be a problem but the drag situation will be better than with 1 engine disabled! After all there is no inactive engine face catching a whole load of air. And an engine failure situation is already a known situation.
Also, if it had failed as designed it would have only lost one. The other one was only lost because the first engine hit it on the way out. As well as the leading edge of the wing and the slats. The plane was doomed but not because of imbalance. It just could not fly under 270 knots.
as the aircraft was beginning its takeoff rotation, engine number one (the left engine) separated from the left wing, flipping over the top of the wing and landing on the runway. As the engine separated from the aircraft, it severed hydraulic lines that lock the wing's leading-edge slats in place and damaged a 3-foot (1 m) section of the left wing's leading edge. Aerodynamic forces acting on the wing resulted in an uncommanded retraction of the outboard slats. As the aircraft began to climb, the damaged left wing produced far less lift than the right wing, which had its slats still deployed and its engine providing full takeoff thrust. The disrupted and unbalanced aerodynamics of the aircraft caused it to roll abruptly to the left until it was partially inverted, reaching a bank angle of 112°, before crashing in an open field by a trailer park near the end of the runway. The engine separation was attributed to damage to the pylon structure holding the engine to the wing, caused by improper maintenance procedures at American Airlines.