its a major event. Potentially heavy or dense material could be knocked out of orbit and fall into a heavily populated area (its unlikely, as it should burn up, but you never know) Its also extremely dangerous for anything else in orbit at present, until the debreefield is dispersed. What you have to remember is these bits are flying in orbit extremely fast. If you were an astronaught and you wanted to fly to the moon you would have to rise through the level where this accident happened, you run the risk of having your ship bombarded by trillions of tiny fragments flying so fast they'd cut your ship to shreds.
Again, hopefully the cloud disperses and the particals dont drop in orbit as a concentrated swarm...or else potentially it would be like putting the International in the Asteroid belt