"Positive. I thought I'd never hear from them again."

Chara doesn't know about the other's Frisk, but their own? Stubborn to a tee. If they'd been a monster, they'd be a puddle long before they completed the first timeline. If you think they laid off or given up? They're biding their time. Or wracking their brains for all the ideas they can, including the stupid ones. Isn't it why Frisk isolated themself from Chara all this time? They should've known Frisk would be back. But if they did, there wouldn't be a future for monsters in their world, would it?