Having worked on the manufacture of the Shutle, I have a fairly intimate amount of knowledge of it's structure.
The TPS - Thermal Protection System, consists of the Tiles in the high energy exposure zones, and a blanketing material
in the non-dynamic exposure areas
There was a confirmed report of a peice of 'Insulation' that had come off at launch and struck the left wing, written off as 'Minor' concern.
If the tiles at the strike impact area had been cracked they may have had portions shake loose from the strain isolation pads they mount on,
or even had an edge exposed during re-enrty that may have allowed aerodynamic overpressures to strip that tile and the adjacrnt tiles
free from the mounts - exposing the aluminum airframe to the temperatures and pressures of atmospheric heating - you have 'Burn Through'
A burn through would have extended on through the structure resulting in shedding the affected wing, and at the point of catostrophic failure of
that wing component, the resulting aerodynamic asymetry would have caused the shuttle to roll and tumble, causing the structure aft of the
crew compartment to shear and open the cargo doors and structuraly disintigrate. That's the senario of how the Challenger came apart also.
40 miles in altitude at 12,000+ MPH is a velocity rate of almost 3 1/2 miles per second, 18,300 feet per second. not much is going to be left.
the major parts that do impact will still be traveling between 200 and 250 MPH when they strike - unsurvivable.
I always thought that the most likely failure would be on re-entry. I was very supprised that the Chalenger blew, and I was standing watching it
climb when that happened. This is a sadly stunning day for our Space Program.