It wouldn’t disintegrate due to a sonic boom, because this extraordinary speed is due to the plane being helped along by tailwinds. If the tailwinds disappear, the plane slows down; it doesn’t speed up.
What I’m not clear on is, would the passengers feel like they just decelerated by 200+ mph in an instant?
Fluid dynamics would spread that deceleration over a short period of time, so it wouldn't be like 'hitting the brakes in a car' type sensation. Passengers may feel a slight shift, but overall, as you explained to the previous poster, the speed is all relative to the air around the airplane.
More likely the turbulence and vortices in the demarcation zone between the jetstream and the different air current the plane enters would jostle and toss the passengers around more than the deceleration would.
From the article, it said the 787 was cruising at 35,000 feet. Seeing as the 787 was built to cruise close to 40,000 feet (above most traffic and weather) I daresay the pilot or company flight planners deliberately asked for a lower altitude based on expected wind conditions. I bet many other airlines were doing the same, leading to a very busy jetstream highway that day!
The jetstream, like all weather and winds, is on a continuum. There is no barrier where outside of the jetstream the air is static. See the principles of flight and how air functions VERY close to a wing for an example. This is actually a good example, though a bit unrelated.
Yeah. Good question. It would really seem to depend on how fast the air speed changes.
I mean, the opposite effect is well attested to - you fly along with a headwind (and sufficient airspeed), then comes along a sudden tailwind, and your airspeed drops sufficiently that you stall, or at any rate descent. Wind shears, often associated with cold fronts or thunderstorms.
Maybe a) mach 1 is further from cruise speed than cruise speed from stall speed, and b) drag slows down the plane more effectively and quickly than the engines can accelerate it.
That could explain why wind shear has and does lead to stalls, but not to sonic booms/structural disintegration.
What I’m not clear on is, would the passengers feel like they just decelerated by 200+ mph in an instant?