I REALLY REALLY REALLY don't want them to kill party members after act one to lock us into a specific party. That would feel very stifling and would drain a lot of the excitement I have for the game.
I haven't heard any news that they've changed the plan, so we're probably stuck with it.
We don't know that "killing them off" is the plan though. An epic 4 vs. 4 battle with the ones you don't choose turning into Illithids could be fun, and that's certainly been foreshadowed several times. But maybe not very believable if we win the fight against what are supposed to be very powerful creatures. It might be that the ones you don't choose just go their separate ways to find their own solutions to the parasite.
The camp itself might also be different in Act 2 and beyond. It would feel weird to keep returning to the current wilderness camp if we're going to be spending time in Baldur's Gate, so maybe the long rest shifts to a room at an Inn or something. That could help justify the loss of the other party members, so they're not all crowding the Inn with nothing to do.