Like it or not, if the Brits/John Company runs things better than the late Qing or Taiping do elsewhere they can hang onto the area for a few decades and even see in-migration (although the sooner legit Home Rule is set up the better for all concerned, and rubbing the "native's" noses in the dirt will get old very fast). The big question is if anything resembling OTL's Warlord Period goes down and at what level responses to facts on the ground get dictated... gobbling the rest of the Chinese Heartland or at least a large chunk of the southern half cannot be ruled out.
Of course the dynamics change a great deal if, instead of direct rule, a more-or-less compliant puppet Emperor (Han by preference, and if christian prone to be both non-heretical and low key about the matter) is enthroned in 'Kuang-chou'. Moreso if the fellow's kids are both bright and on good terms with the local intelligentsia.