Many students whom I have taught are among them, and it's a mixed feeling while we see them go away. Not knowing if or when you will see them again, but feeling good to see them come of age and explore new territories, a la Ulysses, looking for the unknown in the untravelled world. I quote from the poem (Ulysses, by Tennyson)-
The inevitable has to happen, and the young have to find their way. We will be a part of all who we have met!