Snoopy, Joe...
Indeed, it was the Wild Wonder. The coaster was almost brand new when the incident happened. That particular ride had been equipped with a 'quiet' anti-rollback system. Somebody somewhere screwed up and allowed replacement parts for the anti rollback system to be used which were not sufficient for the job. Whether the problem was with Gillian's, or with Zamperla, we may never know for certain.
I don't think the car actually derailed at the bottom of the hill, but it took the curve designed to be taken at low speed...at high speed, and ejected the two riders who were killed.
The incident is eerily similar to an incident on a Wildcat a few years ago at Bell's Amusement Park. This was the older model of Wildcat, similar to the one Cedar Point got rid of in 1979. The Wildcat has a plastic insert in the anti-rollback dog, and that insert shattered under load, allowing the car to roll back down the hill. Two cars collided, riders were ejected, at least one person was killed.
Neither incident involved a chain break.
--Dave Althoff, Jr.