When I have returned to University, I had the same batch of townies as had been there before, but in different roles - my former professor was a student, my former housemate now worked as a barista, etc.
Intergenerationally, I don't know how it will play out. My University Sims have not wanted to have a kid yet. My Sims who have adopted haven't been to University (and their son is still a child).
Try it, and let us know what you find out!