Chara takes that as a yes, which is enough for them to drop it. They got what they wanted.

And it seems they're not going to get any more from him. They can't think of any reason to stay, and they might as well go pester the other Sans, who might have better answers.

"Then I shall get out of it."

His non-existent hair, that is. They stand up fully, and start trotting off.