In our many trips, we've lost/left a few items and Disney has been great.
Once, we left a Disney bag of merchandise on a bus. We realized it within 5 minutes of getting off at our hotel, so called and they had it located for us within about 5 more minutes. On another occasion, left a nice pair of sunglasses. Went to main lost and found location and recovered them there.
The other incident was really weird. Since it was still hot, I had left my curling iron out when we packed to change resorts, then left without it. Realized it later that day and called lost and found. They checked with housekeeping who said that the person who cleaned our room threw it away! I was surprised both that they would throw it away, and also that they would 'fess up to having done so. Within a couple of hours Disney delivered a new curling iron to our room at the hotel we had moved to!
I recall one other instance where Disney lost and found called us after a trip to tell us that they had found some article of clothing -- "green shirt" or something -- that we didn't recognize as ours. I told them thanks, but not thanks, and perhaps to check with another guest.
The last incident was after we had cruised with Disney. Another passenger took one of our suitcases. They realized it several hours later and returned it to Disney, who paid to ship it to us overnight. (I could have waited longer, since it was our "dirty clothes" bag!)