Hi barit1 I think it is HPC that spins contra. The HP shaft is nested inside the well of the IP shaft and the bearings for each have a ~20000 rpm differential due rotation opposition.
TD: From the schematic, the bearings for the aft terminus of the IP shaft are on the shaft side, the Power Arm is outboard of the shaft's end, as it returns foreward, surrounding the bearings. Thus any separation of the Power Arm from the wheel eliminates the cvarriage for the Turbine Disc, via separation, The Disc has no structure left, it is not as if the wheel is inboard, and merely spins on, without bearings.
I have read the report, and it can be read in at least two ways, leaving unclear some of the evidence/conclusion chain of thought.
I have spent hours reviewing the schematic, and to me, it is simple. I might be missing some element, or the drawing may be incomplete or inaccurate. The mate for the Power Arm, Wheel, Shaft, and bearing is in the three lam sandwich at the most aft end of the shaft. If these retaining bolts sheared, the entire Arm/assembly is lost, there is no possibility for any retention of the Wheel's mass for any length of time.
Could you post the Drawing? I have limited computer skill, and perhaps if addressing the same drawing, we could meet in our thoughts? I don't doubt either of you gents, and am in deep water with you two, my mechanical skill is better than my theoretical, and I stand to be corrected, always....