Dissolved CO2 depresses the freezing point - the kegs could very well have turned to slush when you opened them to take a look. It has happened to me with really cold soda, you open the lid and the whole thing turns to slush.
So put the CO2 back on, and try not to worry about it. I think it will be detrimental to those styles of beer, but you won't know for sure until it is thawed.