I've started a run on Nightmare with my Witch Doctor, and I noticed that although I've started with all of my followers and artisans from the beginning, I still have quests that involve me meeting them for the first time.
In the Blacksmith's case, he just disappeared from his workshop and I had to go meet him elsewhere in town. However, my Templar didn't disappear when I met him for the first time in the Cathedral. At the time, I had the Enchantress with me, and they shared a few unique lines of dialog.
What happens if I take a follower to meet themselves? Do they sit the mission out and are replaced by their pre-follower selves?