The attacks on Mumbai create a risk/reward opportunity for international law.
The Risk: The U.S. is emerging from seven years of struggling to form a coherent and pragmatic system for dealing with terrorist attacks. The election of Obama, repudiation of torture ("enhanced interrogation"), Guantanamo, and other policies presented a real chance to create a better rule of law for states to apply in dealing with terrorism.
Just as the U.S. was ready to move forward, one of the world's major powers (nuclear at that), a power who shares a contested border region with another major player in international affairs, is facing the same problem. The risk is that India will make many of the same (mistaken) policy choices as the United States did in facing the challenge of these attacks. This would be a grave set-back for creating a real rule of law for dealing with terrorism.
This path would basically affirm the rule that a state can do whatever it deems necessary to fight terrorism, even by acting outside the law.
The Opportunity: If India is brave enough to respond to tragedy with a cool head, and to insist on a response grounded in law, there is an opportunity to create a sound legal system for dealing with attacks of this nature. All the critiques that people have thrown at the U.S. would be put to the test, and new sate practice would emerge.
Of course, there are already certain legal tools (many listed here), but there has not been an effective development of institutions or a comprehensive legal structure to apply to these situations.
The Upshot: The response to these attacks present an opportunity for the world to create an effective rule of law infrastructure for dealing with terrorism.