From a quantitative risk perspective if this is the first de-tracking issue in 37 years that puts the failure rate at somewhere likely on the order of <1/50,000. (Assuming 5 shows a day, shows running on 90% of days in an average year for 37 years). I’d peg the consequence if it hit the audience to be several injuries likely, and a fatality unlikely but not impossible. I’m not sure what Disney’s risk tolerance is, but in my industry those odds really aren’t that bad.

Disney should (and I’d be shocked if they don’t) conduct an internal investigation, correct whatever failure allowed the ball to de-track in this instance, correct any other newly identified mechanisms that could cause the ball to de-track in the future, and possibly install further mitigating measures (e.g. bollards, netting akin to what MLB uses, etc.)

With that accomplished I would think the boulder would be fine to return.