bear, maybe I misremember, but didn't the reconstruction so far show that the crew choose to slow to M 0.8 in anticipation of entering turbulent air?
More to the point on this item, bear: once the crew verbalized "alternate law" they are aware that they aren't in Normal Law. That tells me that the crew are aware that they no longer have overspeed protection. The crew would thus be aware that they need to be mindful of avoiding an overspeed, since the robot won't be doing it for them.
High speed stability, as I read the chart, would "assist" if airspeed approaches (is close to?) overspeed, but a pilot could override that and make it go too fast. So it isn't a protection, by design, it's more of an assist.
In the Protection mode in Normal Law, my understanding is that the robot would do considerably more to resist the pilot trying to increase speed beyond the threshold value. (Airspeed as sensed by the infamous pitot tubes and massaged vigorously by the various flight control and nav computers. No cigarette afterwards, sorry, this is a no smoking flight!
)
With High speed stability still an available function (presuming that Alt Law was as far as things degraded ... the possible Abnormal Attitude law excursion remains "unproven")
IF erroneous or valid airspeed at the "too fast" limit is sensed,
THEN high speed stability would be expected to make an input to reduce airspeed a small amount. Not sure what that value is.
That's how I read the chart. If I'm wrong, so be it.