I was changing substrate once and accidentally covered one up completely.
A few days after I put down the substrate I got to looking for it and couldn't find it. Checked the floor all around the tank thinking maybe he got out. I finally started digging all thru the pebbles and finally found him. He was in the shell and fine.
This past week I was using a net to scoop out plant debris and accidentally got a balloon molly too. We looked and looked thinking he was hiding but couldn't find him. I went to throw out the little bucket of water and plant debris and when I looked in the bucket I saw the white molly just swimming around. I scooped him up and gingerly put him in the tank and he swam off. I felt so bad but I learned a lesson to be more careful.
I'm amazed how hardy some of them are!!