Give more detail. What exactly do you mean by "gone"? Where are you looking in Lightroom? Post a screenshot of the problem if you aren't sure how to explain it.
Each weekend I import photos from my Nikon D3300 straight into Lightroom. Yesterday I did the same and went into "develop" mode and edited each of them - cropping etc.
And then my 140 photos became just one (see screen shot). I didn't do anything that prompted it. I wasn't trying to export them for example.
Where it now says "Previous Import 1" on the LHS, it had read "Previous Import 140". I can;t under "All Photographs"
I read many of forums and have looked in deleted photos for example - no luck.