Yeah, I played D:OS2 and they did indeed lock you in. I only played with one companion, didn't like the rest of them much anyway so I didn't really care. I wouldn't be thrilled about it here but I could deal with it to be honest.
You do raise some good points though and I think many will be upset if they did that in this game, and if Minsc is an option he'd pretty much be a character I'd never be able to leave behind either haha! I guess if Larian really wants to, it is possible they could die in such a way they can't be brought back with resurrection, or maybe even be converted to the enemy as rivals. Rivals could be kind of interesting at least though?
If I had to pick a compromise, it would be "the party member with the lowest approval of you becomes a mind flayer, leaves, or dies"
Something like that, I think we could all deal with losing one companion... but not being locked into just three.
And there is a problem with the Minsc task, and given Shadowhearts weird box, and Lae'zels complete integration into the story... it just... they might have a bit of a tax to.
I honestly think it might take far more effort for Larian to write a plausible story with all the possibl permutations of three companions, than it would be for them to just keep all the companions.
for gods sake, they have to account for the fact that Gale has a nuke in his chest that can take out a small continent... if he dies, then a continent dies with him.
The Gale Tax is unavoidable.
Every "good" party would probably have to be Shadowheart, Minsc, and Gale in order for there to be anything resembling a happy ending.