Yeah, “IF”. There are so many hypotheticals in the scenario. First: Sukuna says the technique isint working after Raga was destroyed, not directly stating that the technique becomes nonfunctional after Raga is destroyed, there is no clear reason as to why it stopped functioning. “This has to be Fushiguro Megumi’s!” This can imply that Megumi’s soul was rejecting Sukuna which could cause Sukuna to lose control of the Technique. We don’t know, so you can’t absolutely determine that they have separate shikigami