*facepalm*
Dude, the world wasn't destroyed. A great deal of humanity was wiped out by the flood, but the actual planet survived.
Well, the "the world" doesn't necessarily mean the whole planet. The world can also just mean "civilization." Back in ancient times, geology didn't exist, so if you wiped out the whole surface, you were wiping out the known world. In Genesis, it DOES states that the entire world was destroyed by a flood, which makes sense if you use that definition. Also, a great deal of humanity is a bit of an understatement - everyone was wiped out except for the 8 people on the ark, which is eight out probably millions.
At the time of the flood story the size of the Earth was not known. Therefor, the destruction of the entire Earth could not have been certain. It seems more likely that the flood was a massive flood of a small region of the Earth (as known today) even though it caused vast destruction for the time it occurred.
Keep in mind that the earth may have very well been just one continent back before the flood - and after the flood, it broke apart. Before than, covering the entire earth with a flood probably wouldn't have been as big a feat as it would be now.