I have been hunting 20+ years....and unfortunately...it has happened to me more than once...it is part of bowhunting...whether or not we want to believe it. We do our very best to prepare....but nothing can prepare you when you encounter a huge buck....I am not saying that is an excuse....just that you are in a different "state" when encountering a big buck. It sounds as though this buck will live. The best thing you can do is get back out there and hunt. I know you said that your heart was not into it...but it will help you get back in the saddle. It is a gut-wrenching feeling that no hunter wants to experience.....but as others have said...hunt long enough...it WILL happen!!