Chris Scott,
Your quote : Turbine_D, would the fan casings have any tendency to float?
Potentially, at least for a short time. It would depend on the damage. The reason for saying this is the aluminum honeycomb structure sandwiched between the 360° dry kevlar wrap and layer of 360° graphic epoxy and the aluminum inner case (next to the fan blade tips). If the structure stayed partially together for a portion of the circumference, it should at least drift before descending to the sea floor. One engine may be different from the other in terms of damage to this structure.
The vertical impact of photographed retrieved engine was so great, and the kevlar is so strong, I think the fan rotor stopped rotating immediately upon impact as the fan disc was sheared from the shaft. I am thinking that 2/3rd of the fan blades were crushed upon impact. I say this because if anything, fans when free tend to come out forward and the structure forward of the fan was also probably crushed upon impact..
It will be interesting to see how the kevlar wrap survived, it will tell a lot of what happened on impact.