Molching is a fictional place; there is no Molching, Germany.  There is, however, a city called Olching, which happened to also be next to the concentration camp of Dachau; perhaps that is what Zusak was aiming for in his writing.  Based on that, the answer would be that no, the bombing did NOT occur, because in reality, the town did not exist.

However, many German cities were bombed during WWII.  The Allies were trying to destroy munitions factories, weapons warehouses, send messages, and eradicate enemy troops.  All of those intents led the Allies to bomb many German cities.  The most notable bombings occurred in Dresden and Hamburg, where thousands of innocent civilian lives were taken as the bombs wiped out most of the cities.  In Dresden, the heat and fires caused by the bombs was so intense that even if you didn't die in the actual attack, many people were burned to death or suffocated as the oxygen in the bomb shelters was eaten by the fires.  So, even though Molching might not have existed, that is about the only part of the tale that was not historically accurate; many Germans died in bombings, and Zusack recounts what might have occurred quite well.  It is a historical accuracy to describe a town being bombed, especially ones close to strategic war points, like the concentration camp that was so close to the town in that story.

I hope that those thoughts helped; good luck!