Surely you will see someone that you may or may not have forgotten, who you will be happy to see. You may even rekindle an old friendship or begin a new one. Also, people change. That guy who was a jerk in school may have gone through an awakening and now is a sensitive, compassionate, loving funny person. You will not know what you missed if you do not go.
Life is very short.
You can never have too many friends and gee, wouldn't it be terrible if you met MR Right. Then you would have more decisions to make and you might be too happy. You should go to the reunion .