I had the same thing happen to my Fiat500e over the weekend. The car is brand new with under 600 miles on it, and I took it for a short drive fully charged at 99% and it stopped completely on the freeway. It froze up. The first warning that came on was something like "energy conserving mode" and then "propulsion system failure" I could not get the car completely off the freeway. It was a terrrifying experience. The car is now at McKevitt in Berkeley where they are trying to resolve the problem. At this point, my problem is that I really don't trust that car and am not sure I want it back. I was so excited to have a car to drive in the carpool lane, but I would not trust this thing in the carpool lane at this point. If it stopped there I would be killed!
I can understand your fears. Curious to hear what Fiat is doing if anything to help. I'd be surprised if they offered a refund but really should.