2. OPT can not be cancelled afte it is approved. You will lost your opportunity to get OPT if you can not graduate in time. You have to extend your F1 before Dec 31 if you feel you can not graduate in time. Otherwise, you'll be out of status and get lots of trouble.
3. Your advisor has to sign on the application.
4. if you graduate in time and get your OPT, you have nothing to do your advisor anymore.