i've found that, barring any distracting ferrous impediments, running a small strong magnet down the grip from the bolster towards the pommel can give you an indication of where a partial tang ends. i sometimes suspend the magnet from a string just above it and move the grip under it, you can detect when the magnetic field 'grabs' and lets go near the tang end. i use a fridge magneted teaspoon
it's got one heck of a strong magnet in a teeny round disk and a hole in the handle.... if the wood or stag is thin enough the magnet may even stick thru it and suspend itself until you slide it past the hidden tang... not very good for finding anything but how long the tang is, but that in itself is a usefull tidbit.
it may be a press fit, or their may be some cement further up the grip cavity holding it in. unless it loosens on its own, it would probably be destructive to mess with it physically, thermally or mechanically. an xray might be informative. might not too. probably not worth the expense....