That is really interesting. I wonder what will happen in multiplayer if I decide to be the villain and the rest of the party plays good?
Probably something similar to what happens in a PnP game when one player wants to play differently from everyone else.
Unlikely. In PnP, that causes massive problems for the DM. Here we don’t have that limitation.
If I am playing in a multi-player BG3 game and a player wants to play the game differently from the way I want to play the game, I'm not going to play with that person. So, yeah, likely. That's how it works in MMOs. Won't be any different here.