It would be good if Socrates can philosophize with the souls of the dead. Thus, if Socrates can philosophize with the souls of the dead, then death is good. Therefore, if death is a migration of the soul, death is good. If death is either an annihilation or migration of the soul, then it is good. If death is good, it ought not be feared.
Death is either an annihilation or migration of the soul.
Therefore, death ought not be feared. It is something one does with the whole being. It is, for Socrates at least, the most important way to live one's life.