Fatsia japonica is hardy in our zone. Cavendish is not hardy here so you better pot it up or put it in the garage or basement wrapped in news paper and plastic.

The fatsia you can leave in the ground.
The Cavendish banana you will have to bring in.
Even though they are both zone 8 plants. Fatsia japonica has been proven hardy. But I don't know of anyone that has left a super dwarf cavendish in the ground. You could try it. Several other zone 8 bananas will survive a few years but eventually die out.
Maybe someone else has input.

Here is a link that might be useful: Super dwarf cavendish banana