This is partly inspired by the discussion about Maratha India while considering the possibility of Britain still managing a partial conquest.
In other words: if Britain (or the East India Company) had stopped, or rather, had been stopped, in its total conquest of India, where and when would have been that most likely stopping point, and what frontiers would be drawn from there, assuming that Britain would retain the territories it had conquered so far?
How would the interaction between the independent kingdoms/confederations of India and the British Raj fare across the 19th century? Would further strife or mass population movements occur?
As an extra question: what role could be played by other (I'd assume mostly European or Asian) stakeholders in interacting with the independent part of India?