The snail is still alive. I have done a bit of Googling to try to find out if it's even possible for him to regrow his shell, (not likely) and how long he might survive without a shell, (not long.)
I am just hoping that his primitive mollusk nervous system precludes or at least minimizes any pain for him. If I knew he was suffering, I would euthanize him. For now, I found this page on how to make a pet of a garden snail, and I'm following that for his housing and care.
And, I do know that snails are hermaphrodites, meaning organs of both sexes are present in a single individual, but I don't want to call my snail an "it", so I'm calling it "him". If he survives past a few days, I may give him an actual name.