Well, to all appearances, Snaily did not make it through the night. I suspect he has Joined the Choir Invisible. That Snail Chariot has come for to carry him home.
I gave him some more water and nudged the lettuce toward him; I’ll let you know if any signs of life appear.
Long ago, I found some seeds in my, um, herbal tobacco. I planted these seeds, and verily plants did begin to grow.
Placed upon my window ledge they were easily seen from the street and blocked out the light, so I thought it best to replant them in a remote copse with no public access that I knew of.
Fast forward a few days. It turns out that snails like nothing better than herbal tobacco, this must be the case because I’d never seen a real snail before and yet gazillions of the happy little devils (these too were tiny) swarmed (can snails swarm?) over my plants.
Cutting my losses I thought, “Hey, free pets!” and took some home where they lived in a jar to be fed on lettuce. They lasted about a week.
I have never trusted snails since.
Unless you can actually see shriveled eyestalks or foot, the snail may be fine. They can stay sealed up in their shells for days.
Re-Water
Land snails need a damp environment. However, they are air breathers and cannot swim. One site by a commercial farmer described using a kind of moat to keep them contained.