Outside of ASB it is not going to happen. The only way it might happen is if the British decide to largely exterminate the local inhabitants. Another (ASB) option to keep Britain and India united might be for India to become part of the UK in the same way that Scotland is but then effectively the UK part of the British Isles become an Indian province (given their relative populations).
ASB it is.
Even having "India" in its pre-independence definition as a Dominion or Dominions is hard enough.
That includes India, Pakistan, Bangladesh and (I think) Sri Lanka.
Various configurations of independent countries, from a single federal state to multiple fragmented states (Punjab, Hyderabad, Kerala, a Tamil state, etc.) are possibilities.
But any of these various outcomes have independence for however bits emerge from the chaos as a given.
An outlier would be a small part remaining as either a dominion, or an dependency - equivalent to Goa for Portugal.
In a ATL where Singapore, Malta, Gibraltar, Socotra etc. are retained in the French model, i.e. legally as part of the U.K. with full citizen rights, voting rights, and members of parliament, then possibly Ceylon/Sri Lanka?
Would need a big change from OTL though - much better performance in world wars or they don't happen at all, not in hock to the USA, very fast footwork diplomatically and far sighted planning with and for colonies. Pretty much ASB, but not quite.