You will eventually lose the toenail after you get a black toenail. About.com user Sarah's toenail was shed a month and a half after the trauma. The black toenails I've had took weeks to begin to detach. The replacement toenail slowly grows and pushes away the dead black toenail. The new toenail often grows in thin and grooved. It will take several months to have a normal-looking toenail.
Preventing Black Toenails
Getting Shoes that Fit Well
Lace your Shoes to Prevent Black Toenail
Fixing Your Feet: Prevention and Treatments for Athletes, John Vonhof. Wilderness Press, 2006.
Guide Review of Fixing Your Feet, by John Vonhof