In the absence of injury to other bones and ligaments, the removal of the radial head is routine surgery and does not impact elbow function.
The impact on fibromyalgia would minimal and dependent on the amount of stress you put on yourself.
Now should there be the need to install an implant to stabilize the joint, or other procedure, I still cannot see any significant negative effect in regards to fibromyalgia.
Try to relax and see this as another stepping stone towards improvement.
It will all be behind you soon.
Fibromyalgia is not a life sentence and there are many things you can do to
to alleviate its symptoms and live better.
There's an old thread which I started a few years ago titled "IWILLDOTHIS"
where there a lot of good suggestions.
Just go to the magnifier icon -just above your post and do a search.