It's not ideal, but I think you'll be ok. I had four kegs of beer freeze in the back of my pickup while I was driving to a beer festival a couple of years ago. (it's amazing what four hours in a 30 below weather will do). It's not ideal for the long term flavor stability of the beer, but I think it'll survive. For the beer that is carbonated you may find that it's gone flat and may need more CO2 added. That was my experience anyway.