I'm gonna throw in with the lot that says forget the letter and fade away.
A couple of reasons: Why play by their rules? Why give them that authority over you? If you just quietly fade away, you can still associate with your mom and even some of your old pals (if you want). DAing yourself means to accept their definition of who can or can't associate with them. Why give them that satisfaction?
You're a smart kid and wise beyond your years. Just remember though that some things that are done can't always be undone. While you may feel that you need to DA, if something like that just kills your mom and strains your relationship to the breaking point, why not consider her and your relationship with her in the coming years. Fading may cause you a little hardship but it may pay dividends in how your relationship with your mom will be 5, 10, 15 years from now.
But, if you feel that DAing is what it's gonna take to break completely free then you must do what you feel is right for you.