With advances in surgical procedures today brain surgery usually goes through without much if any problems and you have a pretty high chance of surviving brain surgery if it's done by the best surgeon who really knows what they are doing.
Brain surgery is one of the most complicated surgeries and the brain surgeon will have a lot of experience and if the brain surgeon has performed many other successful brain surgeries then your chance of surviving the brain surgery goes up.
It's estimated that brain surgery has a 95 to 96 percent survival rate but of course anything can happen and it's a good idea to be ready for death just in case it happens.
But still even if you need brain surgery and are about to die without the brain surgery then your chance of survival is much higher by having the brain surgery.
My coworker went in for some brain surgery after a car accident and she is doing fine now even though she wasn't expected to make it.