Ouch, sorry to hear that!
Most roosters would be considered to have proven themselves by then.. and be very valued members of their flocks (including the keeper).. generally only the good boys make it THAT far.. maybe he's earned the benefit of the doubt??
I'm not a proponent of one being ousted due to underlying health conditions that might attract disease or predation and somehow only the flock (or lead) can detect.. but do have to wonder why the sudden change at a decent age.
Azygous even has some good information when one is "asking" to be bullied (or somehow accidentally inviting it) how to build their confidence back.. that may be just as helpful as all of our suggestions to cull either by re-homing, harvesting, composting, etc..