The Celtics remain a competitive team through the 1990s, due to the survival of star player Len Bias. Also, a lot of people stay out of prison - the drug war probably isn't as bad in this TL.
I will address Len Bias' survival in my alternate basketball timeline where Bird and Dr. J become Knicks teammates
But Bias doesn't become a Celtic, he goes to Seattle 'cause they had the 2nd pick before they traded it for Gerald Henderson
As for the overall crack epidemic, I think it's ASB to completely wipe it away because it is really easy to turn coke into crack. However, drug law changes could mitigate its effects