Megumi is not dead. This is almost certainly misdirection by gege. I been saying Megumi will be Sukuna's undoing.
Now that Sukuna has supposedly abandoned megumi and reincarnated into his og body, we're supposed to think Megumi is RIP. And this will make the moment when Megumi in his hate and will against Sukuna, suddenly takes control of the body for a split moment in a dire situation, probably when Sukuna is fighting against/ready to kill Yuji, all the more "surprising". That will give the necessary opening for Yuji to beat Sukuna.
Remember when Geto's body reacted to Gojo while Kenny was sealing Gojo? Something like that might happen again. Even if Sukuna is in his of form, the base of the body should still be Megumi's.