If I were representing the family, I would attempt to have the fencing, new signs, etc. admitted into evidence under the exception in Rule 407 for proving, if contested, the "feasibility of precautionary measures." If I were Disney, I would attempt to get around that exception by stipulating (i.e., not contesting) that fencing and new signs were feasible precautionary measures.
As a practical matter, if I were representing Disney, I would do everything in my power to keep this away from a jury. As this thread has demonstrated, it is very difficult to predict how people on a jury might react. For example, some folks believe, based on the limited facts available to us at this point, that this attack was a freak occurrence that nobody could have reasonably foreseen. Others believe the attack might have been prevented through a combination of more explicit signs, better animal control, and stricter enforcement of rules prohibiting the feeding of wildlife.
My practice does not involve personal injury/wrongful death cases, but in every case I certainly advise my clients regarding the value of eliminating that uncertainty with respect to liability and damages.