Even if you lose an item it's relly easy to retrieve it as log as you know where it can be found originally:

1) In your current game walk up to the location of the item and save to a slot. make sure you are not too close to any NPCs to not get stuck in them
2) back up the folder of that save slot (this is important, we will need it later)
3) start a new game with any character and save to the same slot overwriting the old one
4) from your backup copy the file PLAYER.DAT into the new save. This will replace the new character wtith your old one, including class, level, stats, inventor and location
5) now load that save slot and you should be where you originally saved with your original character, except this time the dungeon is still reset and you can pick up the item you want. Note that all NPCs meet you for the first time again and all monsters are still alive. This shouldn't be a problem though since you kept your level and equipment
6) once you have the item save again to the same slot
7) now take your backup and put all the files, except PLAYER.DAT, back into the folder of the save slot. You should now be back in your old dungeon with the recovered item.

I used this trick myself to recover the rotworm stew recepie. I don't know if it disappeared from my inventory or if I had just thrown it out somewhere and couldn't find it anymore. Probably the latter