I've wondered, and asked the same exact question. Does Sundance offer an exploded diagram of the plumbing for their tubs? I'd be interested to figure out the weak/extreme/exposed points in the pipes. It seems likely that the body of the tub could still be 80 degrees, and the pipe on the furthest corner could freeze. (Just like you never worry about your water heater freezing in the winter, it the pipes leading to it...)
Anecdotally, I haven't read anyone with experience of a power outage beyond 3 days recounting their story of whether or not their tub froze on them.