To get it apart, figure on replacing the tang nut. It likely was slotted, then after tightening, ground flush. So the way to remove it will be to carefully drill two holes in the nut, one on either side of the tang... 1/8" maybe? Then take either a spanner wrench that happens to fit or make one by drilling matching holes in a piece of scrap metal and inserting pins to correspond. I'd make the pins out of tapered pins, and such that they would be snug to the hole.
If you get lucky, they won't have epoxied the tang nut in place. If so, you'll have to heat it.
Once you get another tang nut, and figure if epoxy will do what you want, reassemble. Once it's dry, and to suit, grind the tang nut off flush with the pommel and polish it back up.
Most of it could be done with a drill and hand tools, and a belt sander of some sort for flushing the tang nut. I spose you could hacksaw it close and file it and sand it with sanding blocks if you don't have a belt sander.
Sounds hard, but it's not too bad if you don't run into trouble.
Id put a dab of epoxy on the handle layers when reassembling so they don't slide, if there is play in them. Not enough to squeeze out.