Take it to a Sprint repair center. If they can fix it, it won't cost you anything with insurance. Otherwise it's $35. If it's beyond repair (I doubt it), you have to pay the deductible (assuming you have insurance).
While they might not check if you have root (especially for physical damage), they have every right to deny you your warranty if they do find out. That's not to say that they will, but you have no reason to risk it. Unroot first, then root again later.