I don't know about these specific floats - the technology could've changed since the time that I worked around them - but they weren't really built to go in reverse. Also, the cameras and things to help the drivers navigate around the hub and over the bridge into Liberty Square were generally only for forward-moving guidance.
If I had to guess, the floats in front of the Dragon kept on moving as if things were normal, and the floats behind the dragon went into hold/loop. Usually, when a float breaks down, you try to tug it out as fast as possible to keep the parade moving. There's also a chance that any floats/units that hadn't stepped off at that point would've been held in staging and not sent out. I haven't seen this parade except for one time when it first opened, so I'm not sure where in the unit structure this float fell.