What happens if a follower meets themselves?

Question

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?

Answer 1

As mentioned, they follow you for a time as they did the first time, and only after where it would have asked "Do you want X to join your party" the second disappears. The brief bits of bonus dialogue are as follows:

Double Templar

After releasing and talking with the "Warrior"

Templar: Why have you come here, brother?
Warrior: One of our number has forsaken his vows and joined the demonic coven that infests this fallen cathedral.
Templar: Damn that traitor! We will make him pay.

After re-arming

Templar: Evil cowers at the sight of just one templar. Two will bring it to its knees.

After killing Jondar he simply waits at the top of the steps then disappears.

Double Scoundrel

After meeting the clone:

Scoundrel (1): Wait, aren't you from the guild? How could I forget a handsome devil like you!
Scoundrel (2): Why, yes, of course! It's good to see you again!

He simply leaves when you start his quest at the waypoint.

Double Enchantress

After getting the first quest from her:

[Your] Enchantress: She seems very familiar...

At the roadblock:

Enchantress: You must be one of my sisters! How wonderful it is to see you again.

After the bridge she simply leaves.

Answer 2

You actually get both of them for a while, during the time where the follower isn't officially under your control. At the point that the follower would normally join your party officially, the second one disappears and you're back to just your normal follower.

Answer 3

Absolutely nothing really happens (outside some short dialogue) and it is pretty bizarre.

You still have to play out the quests as if you have not done them before, even if the followers meet. They don't have any interactions in town either.

For example: I took the enchantress back to town before she opens the bridge, and walked her right up to the other enchantress and there was no reaction.