As long as you have Chaos Magic equipped as an extra skill, you'll be ready for any contingencies. Using Cassiopeia herself is not mandatory.
Yea, it's just this one's a lot more difficult than Garuda which I did with no healers, relying on the occasional potion or 2 that drop, which wasn't always for sure. I don't feel I can exactly do that in this fight since the risk feels a lot greater.