He's about to answer Zangetsu with a faint I don't know mostly because he was told not to interfere and yet there was a lot of action going on at once. The words barely leave his lips with even Tyki tearing his eyes away to look towards where the others are. Something has caught the Mother of Inventions attention and he is already scanning in that direction even if he can't see that far.

He looks towards Papyrus as he successfully knocks out Sans and Tyki rushes over out of slight concern, keeping his distance so that Papyrus can take care of his brother. Even his hand beckons Zangetsu over so he doesn't have to stand over there by himself.

"Unless she's lurking somewhere nearby she likely has left him. You saw it wasn't the visor that kept her within. He was likely unconscious before she let him go." Unless she was still watching them like a creep through the poor skeleton. Yet that is not what worries him the most as he scans Papyrus slowly for any updated information.