It will be fine as long as it is turned on. If you turn it off, it will soon freeze solid and be destroyed. For that reason, the owner will have emptied it and winterized it, and you won't be able to use it until there's no longer a danger of having it freeze up.

I want to visit a cabin this winter, but I'm sure the temperatures will be going below zero F. The hot tub is just outside the cabin on the porch. But I'm wondering -- with the air temperature being that cold, will the tub be able to retain the heat?