Same thing almost happened to me about two weeks ago. Rear tires are getting worn and I was driving the Z and ran into sudden rain storm at about 60 mph. The back end started hydroplaning, I could feel it shimmying side to side as I let off the gas and coasted to about 30 mph and exited the freeway quickly. Car now sits safely in the garage for the winter with new tires on order. Sorry to hear about the loss of your though.