Few pastimes are much more idle than inventing alternative histories, but here is one anyway.
At the moment, slightly less than 80% of the population of India is Hindu, and about 14% Muslims, with the rest mainly Christian, Buddhist and Sikh. The population balance has been very slowly shifting (0.75% per decade) from Hindu to Muslim. If partition had not happened, and Greater India (India + Pakistan + Bangladesh) one nation, the ratio would be roughly 60% Hindu to 35% Muslim.
If other nations with similar balances of mutually suspicious religions are a guide, that would be a pretty unstable mix. Throw in India's cultural and linguistic divisions, and keeping the nation from exploding would have been tough.