Im surprised that no one has mentioned LArian stating this about the companions

"Will companions be interchangeable during long rest?
Yes, at the start of your adventure your recruited companions will be at camp when not in the adventuring party, and can be swapped in and out at camp. Just like friends in real life! After the first act however you are going to have to commit, also just like in real life."

That last part makes me feel like they are gonna do the Act 1 finale of DOS2.