Depends on how they got popular.
If they were popular because they had a smart mouth, never went to class & got high, then you already know why they are unsuccessful.
If they were popular because they were good looking, then they probably are still successful because good looking people usually get opportunities other people can't get.
If they were popular because they wore expensive clothes, then it can go either way. Rich parents can afford to give their kids a helping hand (I'm excluding the section 8 kids who could still somehow afford to always have the hottest clothes and look down on those who didn't).
If they were popular because they had a catchy/fun personality, then they are probably still successful because your personality can get you far.
It also depends on where you went to school and the race of the kids you went to high school with. Sometimes what's popular to most black kids is what's looked down upon by most white kids.