Question from an ancient stupid here....
What's wrong with an "overspeed"?
Increased drag, increased buffet, possibly some decrease in controllabily. Oh, and in the books you're not supposed to go there.
But otherwise?
The DC-9 was deliberately flown to over Mach 1 during flight testing.
At least one 747 exceeded Mach 1, even if that was not deliberate, and returned to tell the tale.
The RAF VC-10s were over-powered, and some, towards the end of certain flights, were taken way beyond the formal Mcrit.... and they returned.
I'm sure there are others.
Now, I don't know zip about the A330. So maybe it DOES fall apart the moment you exceed Mcrit by two percentage points. I doubt it.
On the other hand, when an aircraft stalls, it's like any other aircraft.... it no longer flies.
And I mean when it "physically" stalls (not with various FBW protections having kicked in, and the aircraft is mushing down, but with still some kind of control) but with loss of airflow over the wings, and settled in a nice flat spin.
My uninformed conclusion is that they got in the "stall" corner of the coffin corner, not the Mcrit one.
Christian