It starts at a specific point in the manga, but I can't recall exactly without looking it up. You might want to check some manga forums or dedicated fan sites for the precise chapter.
It's hard to say for sure. Both Sukuna and Gojo are incredibly powerful, and it could depend on various factors like their current state and the circumstances of the fight.
Well, unfortunately, Gojo did meet his demise in the manga. This plot twist came as a surprise and left fans both heartbroken and eager to see how the story would unfold without him.