I'm going to tell my friend's future roommates about his loud snoring.
What do you think they will do?
I expect they will leave my friend alone once they learn about his night habits.
You should cut your losses with your roommate, but don't ruin his prospects of finding someone else to live with. This is a petty act.
I know what to do. I'll tell them how messed up the apartment was when he was around to scare them away.
Telling on your friend to his potential new roommates in order to get back at him is insensitive and cruel. If you didn't get along as roommates with him that is fine, but don't seek revenge.