Krishna’s words

If Duryodhana had chosen Krishna instead of his army during the Kurukshetra war, how would this decision have shifted the strategic balance and affected the ultimate outcomes for both the Kauravas and Pandavas? Krishna gave chosing option to Arjun first not to Duryodhan. So Duryodhan have no choice at all except to accept what Arjun left between the two. Krishna’s words But it is said that those who are junior in years should have the first choice. Therefore, Dhananjaya, the son of Kunti, is entitled to first choice. There is a large body of cowherds numbering ten crores, rivalling me in strength and known as the Narayanas, all of whom are able to fight in the thick of battle. These soldiers, irresistible in battle, shall be sent to one of you and I alone, resolved not to fight on the field, and laying down my arms, will go to the other. You may, O son of Kunti, first select whichever of these two commends itself to you. For, according to law, you have the right to the first choice.' VII Udyoga parva Krishna knew Arjuna will chose him. There is no chance of Duryodhan getting Krishna on his side. Krishna incarnated to remove the burden of the earth with Arjun being the tool as told by him in Gita . tasmat tvam uttishtha yasho labhasva jitva shatrun bhunkshva rajyam samriddham mayaivaite nihatah purvam eva nimitta-matram bhava savya-sachin BG 11.33: Therefore, arise and attain honor! Conquer your foes and enjoy prosperous rulership. These warriors stand already slain by Me, and you will only be an instrument of My work, O expert archer. So Krishna chose Arjuna to be the one who would carry out his purpose,not Duryodhan. My answer is based on Vyasa Bharat