From a game design perspective, a staged wave style fight is a bit done to death, but certainly an improvement on the current situation.
I'm knew to the modding side of these games, but do we have a way to import new animations & or cutscenes?
I like the zombies getting in on the action, but rather than taking out Visas and Mandalore, I think a stronger choice would be to put a strong debuff on them (plauge style, but a long enough charge to last forever, removed after fight ends via script) then have Nihlus draining everyone sans exile in the room the whole fight. That allows the player with a set of challenges, plus an opportunity to strategize a bit, perhaps make some difficult choices, with friendly fire being a real option.
It changes the whole atmosphere of the fight into something tense and desperate instead of spooy and then meh.