Snail is missing part of shell, exposed lung or something

[Weather Report]

Like an idiot I ordered some garden snails online and the seller sent them in an unpadded envelope in a smushed aluminum tray. most of them dealt with it but a few have cracked shells. One of them got it worst and is missing a large front part of the shell, from which is protruding what looks like a slightly veiny bubble of flesh, which occasionally inflates and deflates. He is the most active of all the snails and eats and climbs happily but I worry he may be in pain.
 
Is this fatal? How can I help him?

[Weather Report]

Update: He's grown what looks like a callous over the thing and it's gotten a lot smaller, so it more or less looks like part of his shell now. I think he's going to be alright. Thank goodness.

[princessboo]

I'm really happy for you!
It's a pity there is not a lot of intel about less common issues with snails.
May your snail be happy!