Originally Posted by
agenkin
No, I cannot remove the bolt. The bolt moves in the derailleur hanger, but because the derailleur cannot make a full revolution around the hanger, it cannot be removed unless the screw is free to move in the knuckle. So I have no access to the U clip because it's between the knuckle and the hanger.....
So it sounds like the bolt and hanger threads are stripped (either or both). You might try bracing the hanger and pushing down on the bolt as you turn it and maybe it'll catch a thread and start unscrewing. Though if it's frozen to the body, you still might not get it off.
So, consider carefully sawing through the hanger as far as possible without touching the RD body, then supporting the hanger and trying to punch the bolt and derailleur out. (or the reverse, support the RD and break the sawed hanger off). Once you do that, you can remove the C-clip and try to punch the bolt free of the body.
Or, see if you can pass a hacksaw blade between the body and hanger and saw through the bolt. However, if you own a 3/8" power drill, drilling through the bolt until it separates at the C-clip groove (smaller than 3/8") is the fastest way.
So, it's a two step process, free the RD from the hanger, then see if you can free the bolt and salvage the RD.