I'm with Nick on this one. Why roll if you don't have to? I plan on my floats keeping me dry, should worse come to worst. You do have floats on your ship while flying over the ocean, don't you?
Unfastening the seatbelt isn't that hard, & you should have plenty of time to get them undone, if you do the auto correctly. I've gone through the 'dunker' training, & if you stay calm, it really isn't that bad. Easy to say, probably harder to do.