I am a bit concerned about what will happen to the companions we don't keep. Larian has stated that we need to commit to 3 companions for a party of 4 like in Divinity.
The ones we didn't pick died when Dallis attacks the Lady Vengeance.
So we need to be careful who we want with us after the First Act.
I somehow doubt we'll have a repeat of that. It fit into the overarching scheme/plot of DOS2 because of the Highlander-style "There Can Only Be One" Sourceror/god contest.