Yup, your pot is history and needs replacing.
The knob, however, can be salvaged. They are not welded, glued, epoxied, cemented or anything to the shaft. It was just wedged in there real tight. Yes, they are indeed removable.
There are 2 main types of shafts and knobs that accompany them:
Look at this picture: A smooth shafted pot which requires a knob with a set screw:
And then there's the split shaft type. These are commonly used, and you can use both knobs with and without set screws. The split allows you to bend them slightly outward to make the knob fit on tighter (if it happens to slide off) and conversely. . if its too snug, you can get pliers and give them a little pinch and the sides should squeeze togeather a little. Thats how you get around the set screw, is you tailor the shaft to fit to the knob.
Ibanez Dome knobs are unique in that they dont require set screws like most dome style knobs. Dont give up on your knob just yet, you can always dremel/drill that old shaft out of there. That is. . unless a moron previous owner didn't understand that their pot just needed a little tweaking to make the knob fit and they went and glued the knob on.