Scenario: Nawab Siraj ud-Daulah doesn't fail to bring a tarpaulin sheet, and so the Bengalese gunpowder is not ruined by rainfall. Or, alternatively, the British are less effective at stirring up treason within his ranks and so lose the war .
The BEIC therefore fail to conquer Bengal, and lacking revenue and manpower from said territory are less effective at projecting power throughout the rest of India. The French are correspondingly strengthened, and more able to thwart British expansion in the South.
As per the title, is this more likely to prevent the conquest of India by Europeans outright, or merely delay it? It seems to me that ideal is for the French to be well-positioned enough to hamper British efforts, but not so strong that they can sideline the British completely and so take their place.
Or perhaps, for the French to be in a similar position to the British in the 1780s/90s, ie poised to sweep through India, only to be disrupted by a revolution comparable to OTLs?