Was this not a long-planned operation? How much has India mobilized on the ground? How prepared is the Pakistani Army?
Before Pakistan's shoot-down today India could not claim a casus belli against Pakistan itself, since Pakistan never acknowledged the targeted terrorists as its own and under post-9/11 resolutions an attack against "stateless" terrorists doesn't really count as an enforceable violation of sovereignty. Now, the shoot-down of the Indian fighter can be characterized by India as an aggressive attack rather than a proportionate response - and gives India an excuse for action not just against terrorists but against the uniformed Pakistani military.
(Had Pakistan responded differently - by, say, embracing India's reasoning to bombard terror camps in Afghanistan - India would have no such excuse, would it?)