This is a very rare occurance that typically would result from pretty major failures.
Furthermore any airplane whose sevice ceiling is above 42,000 feet (41,000 feet in Canada for some reason) must comply with a "special condition" for high altitude flight.
This special condition requires analysis that shows that the chances of a decompression is in the order of one occurance in one billion flight hours. So its really not likely.
I've seen the masks come down several times for testing or inadvertantly by maintenance. It really sucks on large airplanes can can take several hours to restow the masks.
As for physical damage, unless you are talking a bomb, again its unlikely. And damage from a bomb typically doesn't need to be repaired. If you know what I mean...