AU Idea
After the truce, Error decides to just move to some AU, and becomes a puppet maker. Ink eventually finds him a few decades later, and the two spend a lot of time just talking and re-getting to know each other.
At some point, the two "fall in love," and Error makes a Paperjam puppet, and then a few years after that, makes a Gradient puppet. Somehow the puppets were brought to life. Since they're magic puppets, their minds mature, but their bodies do not.
Error and Ink were not ready for that, and had to basically scramble to get everything needed to care for two children.
The whole situation becomes too much for Ink, and he eventually leaves Error to do everything alone. A little annoying, and difficult, but Error manages to do a decent job.
Unfortunately, Ink decides that he's bored just sitting around, and basically forces the truce to be broken by everyone involved.
Now everyone sees Error with his and Inks kids, and assumes he kidnapped them, even though they look very much related. So instead of actually doing his job, Error is constantly fighting to keep his kids with him. Because he isn't doing his job, Ink is encouraging too much creation, and none of the unused or abandoned AUs are being erased, so everything is just falling apart.
There's too much in the multiverse. Everything starts to glitch, people act slower, not everything works properly.
I'm thinking of making some new sans decide to become the next Destroyer of AUs, and maybe they think in order to truly be the Destroyer they need to get rid of Error permanently. And maybe Paperjam and Gradient are used against Error at some point. Maybe Ink is a part of it, wanting things to go back to normal or just being there for the entertainment of it all.