As far as we can tell, the findings of neuroscience indicate that our personalities, our memories and our emotions are the result of trillions of neurons firing around in our brains in a very complex pattern. But when you really get down to it, it's all just standard chemistry. All our decisions and thoughts are made by that organ, the brain, which is nothing more than a heap of matter and energy moving in spacetime according to the laws of physics.

When part of your brain is damaged, part of your mind is too. You're not quite the same. You may have lost memories, or a cognitive capability like speaking, or part of your personality. The more damaged the brain, the more severe the damage is to memory, personality and cognitive functions. When the brain is destroyed, we see a complete lack of memory, personality or cognitive functions. The person is dead, and they begin to decay. The brain in that body, and therefore the mind as well, has ceased to function, as surely as heartbeat ceases to function when the heart decays.

Look, I know death is a scary concept and I can understand the desire to have your mind somehow continue existing forever, but as long as there's no evidence for it it's just wishful thinking. Besides, we know this life exists so make the best of it while you're here, instead of worrying about whether you're good enough to avoid being burnt forever or living your next life as a cockroach. See the quote in my signature.