It may not have been just a pure overspeed failure. Given the coloration of the disk there may have been abnormally hot temperatures at the bore weakening it further than the shed speed of the blades.
Yes, a sump fire is a nasty situation, but there appears to be a six-second interval between the shaft separation (evidenced by N2 IPC spooldown) and the IPT burst. Given the gas stream energy still available from N3, that unloaded IPT disc must have reached a very high speed.
The uniqueness of the IP module area may have prevented the massive tangling between blade airfoils and stator vane airfoils.
I perceive a lack of "what if" planning. The detached disk drifted aft until it contacted some static structure (mid frame) and established what designers call a "false bearing", which had low enough friction to permit the disc to continue accelerating. There were no static nozzle guide vanes to clash with turbine blades, thus destroying the driving torque; the blades remained attached as the disk kept accelerating; and the next part to fail was THE DISK ITSELF.
So at least two opportunities to survive the sump fire were lost IN THE DESIGN PROCESS.
Edit: On second thought, I wish to change the word "survive" in the last sentence to "mitigate".