I found Sucheta Mahajan’s Independence and Partition, sage 2000 particularly good on this. The recently published Madhusree Mukerjee, Churchill’s Secret War: The British Empire and the Ravaging of India During World War II, New York, Basic Books, 2010 is fantastic. And well worth a look at is Joyce Lebra, The Indian National Army and Japan, Singapore, 2008 which gives a pro-INA account. Ahmed Akbar’s biography of Nehru is good on the Congress campaign.
My argument would be that the INA was pretty important – especially amongst the Indian diaspora to the east (in Burma, Singapore, Thailand and elsewhere) which was overwhelmingly favourable to the INA - but also as an external pressure that kept up the idea of independence through force of arms, at a time when the Congress leaders were momentarily silenced by being jailed.
Off-list someone wrote to me to say that the Royal Indian Navy mutinies were probably more decisive – which might well be a case in point. The larger picture, I guess would be that the aspiration for independence was pretty much unstoppable by the time that the British government suppressed Congress in 1942.
The course of events was that the British were left sitting on a tinder-box at the end of the war, and the fuse turned out to be the proposed treason trials of the INA leaders held in the Red Fort. Even though his former comrades in Congress were critical of Bose, Nehru led the way in opposing the trials on the grounds that the INA men were sincere but misled. There were mass protests over the trials on a scale that had not been seen since 1942, followed by the RIN mutiny, which made it pretty clear to the British that they could not hold it. Post-war PM Clement Attlee said that the INA was the reason that Britain had to leave – though I think he probably meant it as a broad metaphor for the falling away of Indian loyalty to Britain.