If you touch the operculum gently, and it retracts away from you, he is still alive. Do that underwater though, not out of the water. Removing a snail from the water is a stressful event, and will not encourage them to come out of their shell. If you can, get a breeder box to put him in with a bit of the snail jello or a bit of zucchini. That will keep him protected from harassment, and entice with food all while staying safely in the tank. Just keep in mind that snails will view any handling as a threat, and their default reaction is to retract and stay that way until they know they are safe.