bearfoil
In QF32, the slide of the IPT into the platform likely heated the IP Disc Rim, fir trees, and the IPT lost its blades in this manner. It would explain a loss of P30 forward, first through the Gas Path, and then at the Splines at LP and IP Ball Bearing case. The immense reversal of torque would certainly serve to explain the IP (Shaft) sever, the Overspeed of the IPT, and the sequence of sounds reported. The reversal of Gas Path would explain sound #1, and the second sound would of course be the Explosive Burst of the IPT out the case (IP case).
If I understand this correctly, when the IPT rotor went aft (coupling slippage), the blades started to disappear, therefore there was nothing driving the IP compressor and it began to slow. Then, since there is less and less air entering into the HP compressor, which is running at a N3 of 98%, the P30 drops (stall?) and fuel to the combustor is reduced, but maybe not cutoff completely. Now if the high speed HPC stalls for lack of air, what happens? It is running in the opposite direction of the IP spool.
Also, what do you mean by reversal of gas path and reversal of torque? The direction of rotation of the IP spool reverses? If this happened instantaneously, perhaps the shaft would shear, I don't know as I can't envision this complete process at the moment without a clearer explanation.