I deliberately left Europe out of the picture. Lets say there is a big attack on London: my guess is the majority of the British people (and CERTAINLY a majority of the British press) will blame the British presence in Afghanistan and suggest a pullout. Same for most other NATO countries. Subsequently, there may well be a rise in nativist/fascist nonsense and life will become harder for the various islamists who still get welfare payments (their number is probably decreasing anyway) but it wont lead to a re-invigorated mission in Afghanistan. Or am I completely off?
One can also imagine an attack in China: That would lead to a large number of detained Uighurs suddenly dying in a tragically failed jailbreak, followed by a meeting with the Pakistani ambassador and then the Pakistani airforce will go out and bomb 10 or 15 villages and compounds in Waziristan and desperately look around for some Uighurs they can round up and put on a plane to Urumqi. And more Chinese special forces will enroll in that pushto and dari training school in inner Mongolia or whatever (I hear the Chinese are great at thinking ahead). Still, no immediate change in Afghanistan.