Bruce Barnbaum mentions that if you go too far you can immerse the print in developer to partially restore the image. This works if you haven't yet immersed it in fixer.
In his B&W Master Printing Class (Photo Techniques), he describes using the process directly on the negative. I've used it to correct 8X10 negatives, and it sure makes contact printing alot easier.
Paul, I believe Farmer's reducer has hypo in it. Plain potassium ferricyanide will desolve the silver in the emulsion, but you need the fixer to get it off the paper and into solution. This is my understanding, but the only bleaches I ever use have a halide. Otherwise, when it's gone, it's gone!