Just thought this was something interesting to share. I keep mystery snails and had one that damaged it's shell from crawling out of the tank. I repaired it and he was actually doing quite well for quite a while. It died recently and I was very curious to see how the shell had repaired under the patch. The other snails in the tank cleaned out the shell fairly quickly (or at least before I found it.)
I thought it was really cool to see how the shell repaired itself. (See pics.) One could argue he would have survived without a patch, but... eh, I felt it was borderline. I use plastic grocery bag and Instant Ocean Hold Fast Aquarium Bond Stick. It's a pain in the butt to do it but I like to give the snails the best shot at recovery. My experience has been that they live longer with the patch, but their lifespan is generally shorter than an average snail.