Thank you for asking! First, @karebear221​, as far as an epilogue goes, we originally intended to put the 10 year timeskip at the end of Chapter 11 into an epilogue. However, considering how vital it is to Chara’s arc, we opted to make it a part of the final chapter instead. It really works best there! As far as an epilogue after that, well, maybe you’ll see some art in the next couple of weeks...
Now for the endings; as I always say, you have to get the bad ideas out of the way to get to the good ones. Here are the simply awful rejected endings:
In this ending, Frisk absorbs Asriel’s soul at the end of their climactic battle with the Horrible Beast. However, they can’t bring themself to leave things as they are, and they reset instead of leaving through the barrier. Due to--uh--magical bullshit, there ends up being two copies of Asriel’s boss monster soul. One that Frisk absorbed before the reset, and one that is still inside Asriel when Frisk undoes his death. Since Frisk now has a boss monster soul, they are able to pass the barrier and leave the Underground.
This one is so bad for so many reasons. First, it relies on some cheap magic time-paradox nonsense to get Frisk out of the Underground. Second, it ruins Frisk’s arc. Running away got them INTO this mess, so it’s thematically a poor writing decision to have it end with them continuing to run away. (There’s not much for them on the Surface anyway.)
2. Asriel Absorbs Chara’s Soul
Second terrible idea: After Chara dies of old age, Asriel absorbs Chara’s soul which causes him to transform into a hideous beast. However, this time Chara is nice about it and the two of them work cooperatively in their shared body. Asriel does not leave the barrier immediately, but it’s implied that they may do so someday.
Ugh, I hate this ending! Chara gets what they want, but it’s a terrible ending for Asriel, who ends up being stuck with Chara FOREVER. Asriel is put in a vulnerable position with literally NO boundaries between him and Chara, AND there’s is no proof that Chara has truly let go of their evil ambitions. This one was quickly scrapped since it sent a bad message and didn’t allow Chara and Asriel to change much from the beginning.
We did include an homage to this ending, when Chara comes up with a “better” plan at the end of Chapter 10. Even if it’s less violent, it still is dependent on controlling Asriel. You’re going to have to do better than that, Chara!
3. Breaking the Barrier with the Captured Souls
Third awful ending, and similar to ending two: After both Chara and Frisk die, Asriel absorbs their souls along with the five children’s souls that Chara harvested. He acquires godlike power and breaks the barrier, freeing monsterkind.
For a while I was really stuck on there being an option to break the barrier by the end of the story. The monsters going free was the goal of the original Undertale, so I assumed that would be the best ending for this story as well.
Unfortunately, this meant that despite everything, Chara, Frisk, and the five other children would be sacrificed in the end. It just felt wrong. In the original game, Frisk helps the monsters but NEVER goes as far as giving up their soul. And because Flowey is a vessel (not a monster) he is able to borrow the human/monster souls to break the barrier and then returns them. The sacrifice isn’t permanent. In the Caretaker AU, that option isn’t available.
There is also the moral issue of Asriel and Frisk being stuck with Chara for all eternity, and it’s unfair to the other children who never wanted any part of this.
Eruto was the one who came up with the idea of Chara freeing the human souls to close their redemption arc. My first instinct was to argue against it; after all, freeing the souls meant there was no chance of breaking the barrier in the near future. But in this AU, breaking the barrier was NEVER the goal. It was a part of Chara’s goal, and that goal is what caused them to commit terrible crimes and emotionally abuse everyone around them. In order to show that Chara had truly changed, they had to let go of the souls (and Asriel) of their own free will.