Delta said Sunday a post-flight inspection showed no damage to the aircraft.
Not surprising, as a firework is designed to disintegrate and the outer surface of a plane is not flammable. Bird strikes are probably a higher risk.
I wouldn't be concerned about damage to the aircraft, I would be worried about whether it messed with the avionics.
Many fireworks are designed to explode at altitude. The biggest risk is probably if the firework is ingested into an engine (also a major risk for bird strikes).