That's good to hear your PSA has been undetectable for some time.
My husband is quite new to this ( Prostatectomy booked for 24/11/2017) so we don't know what his final staging will be. All I know is, he wants to get back as near as possible to his life before the C word. I think if we were at your stage we would be happy and start to enjoy our lives again.
There is no point in worrying about what may or may not happen in the future.Life is too short for that. None of us have a crystal ball including the professionals. Try not to get too worried about the stats they are only that and everyone is so very different.