Our Snowy ripped his nail off completely on the 23rd February this year and it's only just fully grown back normal 8 months later.
It was bandaged by the vets for a week and then we went back for the dressing to be changed again, then another week later the air was allowed to get to it.....
After this just for a short period we did however, put vetwrap on it which is a stretchy self adhesive bandage whenever we went out for a walk just to cushion it, keep the muck out and stop him knocking it.