There's not that much ankle motion with cycling. I doubt that fusion would interfere. It just sets the ankle at a fixed position fore and aft.
A year ago I was facing ankle fusion due to end stage osteoarthritis with pain too severe to walk comfortably. I was told that ankle replacement was risky and often just a temporary (10 year or so) fix and not a routine procedure such as hip, knee or shoulder replacement.
I had the initial consultation with a surgeon and he asked if I'd want to try an "Arizona Brace", a custom made ankle/foot orthosis (AFO). I did and that gave slight relief. My orthopedic doctor then suggested a newly approved time release cortisone injection called "Zilretta". Previous conventional cortisone shots did nothing. The Zilretta has been truly a wonder drug for me. The pain is gone.
An expensive shot but Medicare will cover up to 4 injections per year. One every 3 months is typical. Website says intended for knees but my doctor used it effectively on my ankle. Also says "not intended for repeat use" but it is now approved for repeat injection.
Not sure if your pain is from osteoarthritis but if so Zilretta is something to consider to avoid fusion.