Ideal system (imho):
Person A wins ... person B is pissed and coment on it ... person C may try some ranged attack, wich will be sabotaged by person A.
Person B wins ... person A is pissed and coment on it ... person C may try some meele attack, wich will eb sabotaged by person B.
Person C wins ... person A and B will try to sabotage his attack, but both fail in their effort, NPC is dead.
That would be the best system, yes. Each player would see their own dialog animations with their characters in the center stage even if they lost, as if they were the protagonist.
However, even if they could get away with just creating a couple of extra animations and voices and repeating them, it would still be a lot of extra work involved that I'm not sure Larian would be on board with, especially this late in the dev cycle.
Because of the hand crafted cinematics, I'm not sure how they could pull off switching speakers without insane amounts of extra work actually. The only thing I can hope for is that the character leading the conversation "speaks for everybody", so they would say the line chosen by the party.
SWTOR had it easy because in every conversation, all characters were standing in a circle, and devs could just use a script for the camera work and character focus - at least, that's how I imagine they did it. I guess Larian could try ¯\_(ツ)_/¯
