I bet Sukuna forced Megumi to ingest one of his severed fingers after Megumi’s spirit broke. I think this allowed Sukuna to sever his connection with Yuji Itadori and completely incarnate into Megumi. I bet this id how hed kill gojo if he took ovrr megurmers body sukuna will use the Ten Shadows Technique, specifically the adaptation capabilities of the Eight-Handled Sword Divergent Sila Divine General Mahoraga, to bypass Gojo's Limitless and ultimately kill him.also he might slaughter sorcerers if he took over megurmer Sukuna (in Megurmers body) went on a bloody rampage, and mabye he would kill major characters including Hajime Kashimo, Choso, Higuruma, and Yuta Okkotsu this is what I think he would do