The whole reason Northern Ireland exists is because a majority favour the Union, as expressed by election. The UK has no interest in holding Northern Ireland against it's will. Casting off Northern Ireland when a majority want to remain a part of Britain would be wrong. Admittedly there's a lot more to it than that, but I don't want to drag the discussion away from the intended topic.
Don't compare NI with Palestine. NI has the Unionists, Palestine doesn't have pro-Israeli-occupation-ists.