Near the end of the game, I needed a knife to cut a rope. There was none in the inventory. I picked up a knife at the Lighthouse. It was still in the inventory before the castle fire started. After leaving the burning castle, it was no longer in the inventory. I could not finish the game. What a disappointment that was!

You could ask for a save over in Hints.
Also, sometimes items reappear in games after you leave the game, reboot, and start the game again.