In my vagrant game, I collected all the components for the JD sword in SOA, but I did not forge it then, as I was worried about the difficulty of the battle I would have to face. Hence, I decided to postpone the forging to TOB. This is what occurred:


After facing the battle in the Oasis, I went to the Watcher's Keep to complete the Demogorgon battle, following which I went to the WK outdoors. I Pocket Planed and forged the JD, which told me I had to defeat so-and-so within 7 days, and I Pocket Planed back to WK again. Met the Demon Prince, chose the first dialogue option. Here's where it got strange:

My protaganist was wielding the sword when after a round or so, it disappeared! I have played the game legitimately and without cheating, so this came as a shock to me. Even so, after a few reloaded attempts to prevent the sword disappearing (putting it in my inventory instead of my weapon slot etc), I decided to go through with the battle and see if I could get it back. I didn't, even after wiping out the Demon Prince and his whole bunch of summons (which was rather tough without the sword).