Mystery snails need some bare glass or a closed hood to lay on. If they go looking for a spawning spot and one is not closely available, they keep looking. That's when they might fall off the glass.. they try to crawl to the outside and can't hold on. They sure can't live a week out of water. A few hours at best, and I've had them die after a very short time. Even though they breathe air, they have to open their door to do it, and the body dries out too fast. So they either die by dehyration or by suffocation. Poor things.
If you want eggs, provide a place for them to lay eggs. Bare glass, 2 or 3 inches at the top, or add a glass piece that they can get to, that sticks up that high above water. Or tile or slate, even wood.. somewhere they can reach that's dry and above water, where they won't be at risk of falling off.
