It's really funny to me to see people trying to come up with all kinds of convoluted spin to try and justify Larian's choice about locking us into only three companions and no more after Act 1. There's really nothing to explain or justify. It is absolutely a terrible game design choice, something that fundamentally takes away from the roleplaying element of the game and thus degrades the game as an RPG. My only hope here, just as with too damn many other aspects of this game, is that it can be removed/fixed with modding.
I got from the answers here, that even the people, who are ok with a smaller cast of characters are not ok with killing Off the companions, that aren't in the group by the end of act 1. I did understand, that no one likes the idea of being stuck with three companions for the rest of the game.
Given the similarities with DOS2 it would not at all surprise me if the companions are not killed off - rather I imagine they will show their faces again later in the game. They will be corrupted by the tadpoles, full blown Mindflayers, bodyguards to some big bad or something like that.
