Its likely that the charges will be either dropped or reduced as long as you go to Court and ask to drop the charges in front of the Judge. It will also help if he goes into a program for alcohol and completes it.
You may want to consider (after reviewing the matter with an attorney) telling the prosecutor that if they don't drop the charges you may not be available to appear in court as a witness. If you are their only witness, they will usually drop the charges, however, you must be careful because I've also seen some prosecutors charge witnesses themselves if they refuse to appear for trial. That's why you need to have an attorney advise you on this.