No, that is a not a determined will . . . it is a warning. If it were a determination, there would be no need for a warning that God worked so persistently to get Jonah to deliver. The reason why God sent Jonah to Nineveh was to warn the people to turn from their evil ways. That warning is a huge part of God’s plan, again as stated here.
“If at any time I announce that a nation or kingdom is to be uprooted, torn down and destroyed, and if that nation I warned repents of its evil, then I will relent and not inflict on it the disaster I had planned.” (Jeremiah 18:7-8)
So, again, if they turn from their evil ways, they will be spared, as part of God’s plan. God will relent from the destruction He warned about. If they don’t turn from their evil ways, they will be destroyed, as part of God’s plan. You cannot simply ignore the one at the expense of the other. The two parts go together, as the Jeremiah verses show.
As it happened, they did turn from their evil ways and thus God did relent, i.e., let up, on his threatened destruction, as stated in Jonah 3:10.
“When God saw what they did and how they turned from their evil ways, He relented and did not bring on them the destruction He had threatened.”