מִֽי־יוֹדֵ֣עַ יָשׁ֔וּב וְנִחַ֖ם הָאֱלֹהִ֑ים וְשָׁ֛ב מֵחֲר֥וֹן אַפּ֖וֹ וְלֹ֥א נֹאבֵֽד׃
Who knoweth whether God will not turn and repent, and turn away from His fierce anger, that we perish not?’
Malbim on Jonah
Who knows but that God may turn: ... from the fact that God sent a prophet, the king understood that their repentance will work.