I have been wearing a full face helmet for 5 or so years now after an OTF crash that introduced the tip of my ski to my face. The ski won, crushed the right side of my face and blew out my orbital cavity. The result was 3 separate surgeries, a month or so in the hospital and lingering vision problems with the one eye. I have had a couple of good crashes since then and have not noticed any interaction of the helmet with the water during a tumbling fall....I do think about it though
To each their own. I cant bring myself to ski without a helmet now (not sure a second repair of my face would take!) My kids are now starting to slalom and they will wear helmets. I don't believe their use will ever be mandated. I found the above article interesting even if it doesn't set me completely at ease.