All the monster have been set free but after a certain time some monster begins to really sick ,Alpheus made research and she discovered that the body of that monster needed magic and on the surface it was really hard to absorb some ,so some monster to stay alive needed to go back down but the barrier still open and they can't come and go like they want .toriel have moved on the surface and she live with frisk in the countryside they continue to see the rest of the group but after time most of them get back in the underground except alphas you have an apartment in the city need the countryside and live at Undyne house when she's in the underground . Toriel want to frisk to go to school and have a normal life of human so she send her daughter to a boarding school .at first this idea didn't make Frisk happy but she became used to it and she know that her mom loved her . After many years, Toriel began to be sick at her turn but she didn't want to go back before frisk finish her school graduation, when she will be 18 years old.