When you say that you tried the knockout rod, what does that mean?
Presuming that the tailstock is hollow, you should be able to insert the knockout rod far enough for it to tap the back of the stuck mandrel saver. The principle behind the use of the knockout rod is that you should be able to impart enough energy into the male portion of the morse taper to break the friction fit just by snapping it into the spindle. But if things are really bad, there's nothing wrong with tapping it gently with a wooden or rubber mallet.
You said something about the bearing cap on the mandrel saver coming loose - that almost suggests that the mandrel saver has failed (and probably is a throwaway at this point), which means that it could take more force to remove it. But you want to minimize the damage to the female morse taper. Obviously, after you get everyone thing apart, you need to inspect the female fitting very carefully, and if there is serious damage you may be forced to use a reamer to resurface it.