The permanent identity is often seen as the "soul" or the "higher self" not the worldly self. The lower or worldly self is usually not worth keeping! Certain individuals purify their mind and personality and continue on as JC and others like Buddha proved. There are parts of my own personality that aren't worth immortality and I will be happy to see them die off, but the higher and purer self/soul will continue on. The exact facts can't and shouldn't be known. The Earth is out testing ground and the universe is our university so it would be wrong to see all the answers before the test is over.