I understand your anxiety. I am now 58 and when I was 53 I had the exact same situation as you. I read everything I could get my hands on and most of it scared the heck out of me. Let me suggest that you get several opinions and if surgery is warranted find the best surgeon who specializes in this type of procedure. Rest assured that in most situations you will be back riding without any problems in no time.
I was operated on and it turned out that I had a cold nodule but half my thyroid was still functioning. I think you will find that people who take synthroid, once they are in balance, are absolutely fine.
If you are like me (and most people) you must have a great level of anxiety at this point but rest assured in the great majority of cases this is a very recoverable situation.