Most Helpful Guy
You should go, he might want to say something important there.
Should it end up being just a friendly meet-an-greet I would do one of the following.
A - The choice I personally wouldn't go with
Stay on as a friend, but don't get used.
B- My personal choice based off of things you said in your question
The hard choice, to stop talking to him unless he initiates talking, and even then not delving to deep into conversation and then cutting it off after 15-20 minutes by saying that you have to go. but never really giving a reason why. Slowly he will stop talking to you and will allow/help you to move on sooner, while not just cutting the ties and breaking them off in a necessarily bad way.
Most Helpful Girl
Unfortunately it's impossible to say if someone will come back... plenty of people cling onto that false hope and then years down the line realize they were wrong and that they missed out on so many opportunities due to them hoping for their ex to come back. I think you should go and see what he has to say. You don't have anything to lose by just going. If it doesn't go the way you hoped then it's time to decide if it's worth waiting for him or not... most of the time it's NOT worth it. You're just prolonging your pain.