I forgot to ask about the percentage of the bark that is normally lost and was told that the bark would get louder over time.
It really depends on the vet, and the exact technique used (there's a bit of an art to it; different vets will make the puncture slightly differently). I would say that with our vet in CT, there's maybe 50% of the bark left? It's hard for me to figure it in terms of a percentage. It's more like the "sharp" part of the bark is rounded off - so it's not that it's that much less loud, it's that it doesn't carry as much. Does that make sense?
Some debarks sound like a raspy "rah, rah", others will sound like a "woo, woo", or even like a seal's bark in a movie soundtrack. Sometimes you'll get a harsher "arf, arf".
I'll reiterate that the dogs bark just as much, and in the same contexts ("Mailman's here!" "Hi, Mom!" "Faster with the cookies!"); it's just the sound that changes. They will also continue to make other normal vocalizations (gentle woofs, alarm barks, whines, yelps when hurt), which you will be able to recognize as needed. The projected bark just doesn't carry as far as before.
"Regrowth" also depends on the vet, and on the individual dog. I don't know that I can predict whether or how much change you will see. It is entirely likely that the bark he has now is the bark he will have.
The best thing to do would be to ask his breeder. She has probably used this vet for other debarks, and can tell you more about what to expect.
I can say that I have spent the better part of my life around debarked dogs, my own and other people's. I've lived with debarked Shelties, shown debarked Shelties for other people, and assisted handlers with debarked Collies. I know that, on paper, it sounds like a bit of an alarming surgery, but I encourage those who are skeptical to actually spend time with dogs who are debarked, instead of just considering it on theory. They are perfectly-ordinary dogs, who do very ordinary dog-things (aside from, usually, living in a slightly larger dog-household). They aren't depressed or rendered uncommunicative. They just don't bark as loudly.