I was playing the game normally when I accidentally threw my Diamond Sword throught a Nether Portal, and when I travelled throught the Portal, the Sword Disappeared. I travelled back and nothing changed. Lost my sword. There was a Villager in the Nether right in the Portal, but as far as i know, Villagers can't take Swords.
I don't now if this makes any difference, but the Sword was with a Custom Name; Mending; Fire Aspect II; Unbreaking III; Sharpness V; and Looting III.