Yes and I answered it above, in reality any invasion would lead to immediate conflict which Britain would obviously win so the questions entirely theoretical.
However in the theoretical outcome you describe we have to take history as our example, so we can safely conclude that over hundreds of years tensions would fade and communities would integrate as has happened repeatedly during Britain's history. Mainland Britain left any catholic and protestant conflict behind along with witch-burning (this is literally true I'm not being sarcastic), it simply isn't a thing here anymore. No parallel problem is possible unless you replaced the entire population with people who do care about that sort of thing.
You miss the point its an analogue not your own version, Britain didn`t get the territory back and the Irish territory is a day to day reality and obivious ongoing source of tension.
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