A teenager does not leave a gang by going through any kind of ritual, or announcing that they are leaving the gang. This is a BIG MISTAKE.
A kid doesn't have to "get jumped out." What they have to do is stop engaging in negative, self-destructive behavior: Stop using or selling drugs, stop engaging in violence, and stop engaging in criminal activities. They can do this without any formal "quitting the gang."
Believe me, no one in the gang is forcing your teenager to do these things. That is an excuse. Every gang member I know who stopped engaging in gang activities never left the gang. They still lived in the neighborhood, they still talked to old friends in the gang. They just stopped doing the bad stuff. I know it is hard to believe, but no in the gang forced them to break into homes, steal cars, or even engage in violence. Gang kids are human, and they have real friends in the gang who care about them: While their friends may keep doing these things, they won't hurt their friend who is trying to get straight.
So don't focus on "getting the kid out." Focus on getting the kid sober, employed, educated, and involved in productive activities. THE GANG PARTICIPATION WILL TAKE CARE OF ITSELF!!!
I have worked with hundreds of gang youth for over 30 years. Getting sucked into a kids story that he can't leave the gang will take you down a long, losing road. I tell kids that I don't care if they are in the gang or not. What I care about is that they have a job, a good hobby, something to take pride in, something to make their parents feel good about, support to stay sober. Every single time, as the kids began to live a different kind of life and feel like a normal person with a future to look forward to, the gang became less and less important.
The Gang is not a good influence, but the only way to leave it is to replace it with something better. You can't "leave the gang" if you have nowhere else to go