If it happens it happens. What will be the real test is what country or counties join in the confusion caused by the "bombers" and how much of a chicken sh*t our own government will be in doing something about it.
The more serious thought is that several countries, such as N. Korea, China, Iran, and Russia, might be enabling Al Qaeda with agents, weapons, etc., to use, to that they can knock off the USA without seeming to make war on us.
(So, it's not the terrorist capabilities we have to fear, but the capabilities of the secret services of China, N. Korea, Russia, etc.)