This happened to me too and I felt awful. It was my birthday and I went for takeaway and realised that one of the sapphires was missing from my engagement ring.
Outside the shop was lots of broken glass, so DD and I got down on our knees to search, but nothing.
When we got home, we searched the driveway, but nothing, I was in tears. It wasn't the monetary value, it was what it represented.
I was so fed up at my birthday being spoiled, I opened up a bottle of Cava which a colleague had given me, and at the bottom of the gift bag was the missing sapphire!
I was so lucky as the jeweller who repaired the ring said that it would have been very difficult to match the missing saphire with the one which was left.
I had to get a whole new setting, as I had obviously caught the ring on something.
Please don't give up hope. If you only noticed it whilst at home, that's probably where you lost it.
Good luck!