This question is a hypothetical one, I think Hua Tuo definitely wouldn't have succeeded, and the end result would have been to be killed, death is certain, it's just a matter of how.
Let's not talk about the checkups before the surgery, as if Cao Cao's body is not in any serious trouble, all the body functions are normal, there is no anemia ah, low protein and other diseases. These external factors everything is according to the best value. Then what does Hua Tuo use to open the skull? Where to open it? How big is the bone window? These are all practical problems, which were impossible to accomplish in that era. Well, even if Hua Tuo was great and all these were accomplished, how to stop the bleeding? Post-operative extra-membranous hematoma will not be post-operative infection and so on a series of problems are there, so from that point on it will not be successful at all!
Let's assume, for example, that Hua Tuo succeeded in opening the cranium, in those days there was no basis for human anatomy, in case of which blood vessels, which nerves, how to do? How to stop the bleeding and give Cao Cao fluids in the face of brain tissue, no lighting, and so on? I think this possibility is 0, is impossible to complete, then Cao Cao surgical engineering, must also be due to excessive blood loss, respiratory difficulties or even failure, shock and other symptoms, if these symptoms, then Hua Tuo will certainly be Cao Cao's men clubbed to death!
Oh my god, even if all of this is accomplished, what about the post-operative anti-inflammation? Also, how long does the so-called Ma Bo San actually work to anesthetize the patient, and will Cao Cao be able to resist the excruciating pain if it fails throughout the entire surgery? Post-operative complications, post-operative intracranial infections and many other issues are impossible to get around!
All in all, I don't think Hua Tuo's craniotomy could have been successful, and Hua Tuo would have inevitably been killed for many reasons during, or after, the operation!