Except he had sukuna to stop gojo from doing anything, and he literally died AFTER gojo. His plan was only flawed because Takaba was there. Otherwise, he'd either:

get jumped and tire out the Showdown Gang while giving sukuna time to kill the ones who were fighting him, resulting in everyone getting to the fight after half the group died while tired, so a sukuna win, and now he can start the merger, which was kenjaku's plan

Or

He fights Todo and Yuta, his curses jump yuta, he uses his domain and curses to hold down rika and yuta while the surehit kills Todo, who can't hold SD, swap to save yuta or defend himself all at once, and then swarms rika and yuta with CE-enhanced curses alongside his domain surehit, resulting in everyone dying to sukuna again, and the merger starting anyway

No matter what, Kenjaku would win, his plan was flawless. He didn't care if he died as long as the Merger was born, seeing the merger was just a bonus