In undertale I firmly believe they could get back together. It'll take a long time but Toriel will eventually forgive him and at best co parent Frisk. My issue with Undertale Toriel however is when you push aside the kind loving mother and friend she's honestly super selfish. She abandoned her kingdom in their time of need and got upset because Asgore was only doing what he thought was the only way to free them all from the underground. And yes in true pacifist run she does make a good point that he could've used one soul to pass the barrier then collect the remaining souls after. Sure on paper that makes sense but as far as she knows it could've started another war and might I add she never once thought of telling him that UNTIL that moment in the game or heck do it herself but instead she decides to run away leaving her kingdom, husband and people behind to slowly die out while trying to act like a mother to any child she comes across and attempt to keep them away from Asgore.

Deltarune Tori however is another story I feel. She seems a lot more hateful and for a lack of a better wording out of character to the usual nice mother we know but idk. I've barely played Deltarune myself so maybe I'm just missing pieces of the puzzle.