My QOTW answer

#hpaweeklyquestions

I think some died in a battle against another great dark wizard who is not named

Maybe some left since they couldn't handle it or were sent away by the ministry of magic example maybe with whining Myrtle that the DADA professor has been sent away for not being able to protect the students

Maybe some wanted a normal life and got themselves Dismissed so they could have been with their family again

Possibly most of them died of old age or didn't have alot of trouble/bad intentions towards the students. So they have been working for hogwarts and Dedicated their lives!