are you interested in the ground speed or the air speed?
and are you referring to the maximum operating speed or the speed at which an aircraft would break apart?
also, i assume the fact that an airliner is descending is relevant as a plane that is diving from height can begin with a higher velocity and experiences a lower density of air until the final moment. the thrust of the engine of a diving plane is forcing the plane forwards against gradually increasing air densities rather than a continuous air density. gravity also provides assistance.
so the question becomes more whether it can maintain its speed (or lower the rate of decline) on the way down and whether the aircraft can retain its integrity under those conditions?
also, the answer depends upon how much the ground speed is increased by air movement (ie wind) in the direction of flight.
but put simply, i know of only one example in which an aircraft was tested at the ground speed you suggest while descending fast. the answer was yes.
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