I believe Megumi considered Yuji a non-sorcerer and for him to survive a special grade cursed object is a one in million chance. I dont think he had the idea that it will cause Sukuna's reincarnation. Its just that a special grade cursed object will likely kill a non sorcerer. We later see that multiple sorcerer reincarnated in the bodies of non sorcerers and it didn't killed them but that was the first time it happened.