Joe,
Having to replace the ball joint is the last option.
These fittings are threaded but they can be removed by using an easy-out, available on the Snap-On truck/catalog, local parts stores, etc.
I have also heard of people trying left hand twist drill bits to remove broken fasteners.
You could also drill this thing out to almost the exact size of the threads and collapse the remaining portion of the fitting and remove it that way.
We used to do all these techniques on our airplanes in lieu of actually replacing a major portion of the landing gear. In your case, replacing a ball joint, and getting an alignment done afterwards.
Sonds like someone is trying to get more out of you than actually needed. If you don't feel like doing it yourself, get someone at the local machine shop. These guys get busted off bolts out of blocks for a living, along with the other magic they perform.
My .02 worth.
Cee