Even "Demons in the Punjab" is a bit more nuanced than that, when its implied that its the homegrown Hindu and Muslim zealots stoking up mob rule and ethnic cleansing, while the British garrisons (fundamentally dependent on the arms and training of Yasmin's grandfather, and his murderers) had to pull out when the loyalty of the co-opted Indian bureaucracy and soldiery was no longer sustainable.
What else could've happened? Put off Partition and there'd be no "safety valve" like West and East Pakistan, so the inter ethnic and inter caste fighting possibly escalates into decades of Indian civil war? Maintain British rule through Weapons of Mass Destruction (nerve gasing hill rebels, threatening to nuke cities, etc), Stalin/Mao famines, and industrialized killings on a Hitlertarian scale?!