Given the reality of the Great Mutiny/Rebellion/etc
Given the reality of the Geat Mutiny/Rebellion/etc in 1857-58, pretty clear the British could cope with a (mostly) ad hoc rising in one of the three presidencies in the 1850s, so that's not enough...
However, combine a larger rising (not necessarily better organized, because there's probably not enough of an Indian "resistance" to organize much of anything absent the press of events) in both the Bengal and Bombay presidencies (Madras seems a stretch, but that's another option) ... Combine the above with a conventional war with a Western power (Russia is the obvious choice, France less so in the 1850s) and the correlation of forces are such the British will have to chose one or the other. ... So that gets closer to a loss than any other point, one would expect.
There's a reason the British were always concerned about being involved in a European war and a "major" colonial conflict at the same time.
The 1850s are also interesting because the technological differential between the British and imperial forces and the Indian "resisters" is not as wide as it would be later in the century.
Do we have any Indian members?
Best,